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THE    EFFECTS 


V 


■ 


CROSS  AND  SELF  FERTILISATION 


VEGETABLE  KINGDOM. 


Bi    CHAELES   DABWIN,    M.A.,    F.E.S., 

ETC. 


NEW  YORK: 
D.   APPLETON    AND    COMPANY, 

1,   3,   and. 5    BOND    STEEET. 

1892. 


TS\\e>. 


CONTENTS. 

CHAPTER   I. 

Introductory  Remarks. 

Various  means  which  favour  or  determine  the  cross-fertilisation  of 
plants  —  Benefits  derived  from  cross- fertilisation  —  Self- fertilisa- 
tion favourable  to  the  propagation  of-the  species  —  Brief  history 
of  the  subject  —  Object  of  the  experiments,  and  the  manner  in 
which  they  were  tried — Statistical  value  of  the  measurements — 
The  experiments  carried  on  during  several  successive  genera- 
tions—  Nature  of  the  relationship  of  the  plants  in  the  later 
generations  —  Uniformity  of  the  conditions  to  which  the  plants 
were  subjected  —  Some  apparent  and  some  real  causes  of  error  — 
Amount  of  pollen  employed  —  Arrangement  of  the  work  — 
Importance  of  the  conclusions       Page  1-27 

CHAPTER    II. 

CoNVOLVtrLACE^S. 

Fpomcea  purpurea,  comparison  of  the  height  and  fertility  of  the 
crossed  and  self-fertilised  plants  during  ten  successive  genera- 
tions—  Greater  constitutional  vigour  of  the  crossed  plants  — 
The  effects  on  the  offspring  of  crossing  different  flowers  on  the 
same  plant,  instead  of  crossing  distinct  individuals  —  The 
effects  of  a  cross  with  a  fresh  stock  —  The  descendants  of  the 
self-fertilised  plant  named  Hero  —  Summary  on  the  growth, 
vigour,  and  fertility  of  the  successive  crossed  and  self-fertilised 
generations  —  Small  amount  of  pollen  in  the  anthers  of  the  self- 


IV  CONTENTS. 

fertilised  plants  of  the  later  generations,  and  the  sterility  of 
their  first-produced  flowers  —  Uniform  colour  of  the  flowers 
produced  by  the  self-fertilised  plants  —  The  advantage  from-'  a 
cross  between  two  distinct  plants  depends  on  their  differing  in 
constitution       Pa^e  28-62 


CHAPTEE  IIL 

ScrophulariacejE,  Geskeeiace^:,  Labiate,  etc. 

Mimulus  luteus ;  height,  vigour,  and  fertility  of  the  crossed  and 
self-fertilised  plants  of  the  first  four  generations  —  Appearance 
of  a  new,  tall,  and  highly  self-fertile  variety  —  Offspring  from  a 
cross  between  self-fertilised  plants  —  Effects  of  a  cross  with  a 
fresh  stock  —  Effects  of  crossing  flowers  on  the  same  plant  — ■ 
Summary  on  Mimulus  luteus  —  Digitalis  purpurea,  superiority 
of  the  crossed  plants  —  Effects  of  crossing  flowers  on  the  same 
plant  —  Calceolaria  —  Linaria  vulgaris  —  Verbascum  thapsus  — 
Vandellia  nummularifolia  —  Cleistogene  flowers — Gesneria  pen- 
dulina —  Salvia  coccinea —  Origanum  vulgare,  great  increase  of 
the  crossed  plants  by  stolons  —  Thunbergia  alata         ..     63-97 


CHAPTEE  IV. 

Crucifer^,  Papaverace.e,  Resedacej3,  etc. 

Biassica  oleracea,  crossed  and  self-fertilised  plants  —  Great  effect  of 
a  cross  with  a  fresh  stock  on  the  weight  of  the  offspring  —  Iberis 
umbellata  —  Papaver  vagum  —  Eschscholtzia  californica,  seed- 
lings from  a  cross  with  a  fresh  stock  not  more  vigorous,  but 
more  fertile  than  the  self-fertilised  seedlings  —  Eeseda  lutea  and 
odorata,  many  individuals  sterile  with  their  own  pollen  —  Viola 
tricolor,  wonderful  effects  of  a  cross  —  Adonis  aestivalis  — 
Delphinium  consolida  —  Viscaria  oculata,  crossed  plants  hardly 
taller,  but  more  fertile  than  the  self-fertilised  —  Dianthus 
caryophyllus,  crossed  and  self- fertilised  plants  compared  for  four 
generations  —  Great  effects  of  a  cross  with  a  fresh  stock  — 
Uniform  colour  of  the  flowers  on  the  self-fertilised  plants  — 
Hibiscus  africanus 98-141 


CONTENTS.  V 

CHAPTEE   V. 

Geraniace^e,  Legtjmtnos.e,  Onagrace^;,  etc. 

Pelargonium  zonale,  a  cross  between  plants  propagated  by  cuttings 
does  no  good  —  Tropseolum  minus  —  Limnanthes  douglasii  — 
Lupinus  luteus  and  pilosus  —  Phaseolus  multiflorus  and  vul- 
garis—  Lathyrus  odoratas,  varieties  of,  never  naturally  inter- 
cross in  England  —  Pisum  sativum,  varieties  of,  rarely  inter- 
cross, but  a  cross  between  tbem  highly  beneficial — Sarothamnus 
scoparius,  wonderful  effects  of  a  cross  —  Ononis  minutissima. 
cleistogene  flowers  of — Summary  on  the  Leguminosa?  —  Clarkia 
elegans  —  Bartonia  aurea  —  Passi  flora  gracilis  —  Apium  petrose- 
linum  —  Scabiosa  atropurpurea  —  Lactuca  sativa  —  Specularia 
speculum  —  Lobelia  ramosa,  advantages  of  a  cross  during  two 
generations  —  Lobelia  fulgens —  Nemophila  insignis,  great  ad- 
vantages of  a  cross  —  Borago  officinalis  —  Nolana  prostrata. 

Page  142-187 

CHAPTEE   VI. 

JSolanace^:,  Primulaceje,  Polygone^:,  eto. 

Petunia  violacea,  crossed  and  self-fertilised  plants  compared  for  four 
generations  —  Effects  of  a  cross  with  a  fresh  stock —  Uniform 
colour  of  the  flowers  on  the  self-fertilised  plants  of  the  fourth 
generation  —  Nicotiana  tabacum,  crossed  and  self-fertilised 
plants  of  equal  height  —  Great  effects  of  a  cross  with  a  distinct 
sub- variety  on  the  height,  but  not  on  the  fertility,  of  the  off- 
spring —  Cyclamen  persicum,  crossed  seedlings  greatly  superior 
to  the  sell-fertilised  —  Anagallis  collina  —  Primula  veris  — 
Equal-styled  variety  of  Primula  veris,  fertility  of,  greatly 
increased  by  a  cross  with  a  fresh  stock — Eagopyrum  esculentum 
—  Beta  vulgaris  —  Canna  warscewiczi,  crossed  and  self-fertilised 
plants  of  equal  height  —  Zea  mays  —  Phalaris  canadensis. 

188-237 


VI  CONTENTS. 


CHAPTER   VIL 

Summary  of  the  Heights  and  Weights  of  the  Crossed 
and  Self-fertilised  Plants. 

Number  of  species  and  plants  measured  —  Tables  given  —  Pre- 
liminary remarks  on  the  offspring  of  plants  crossed  by  a  fresh, 
stock  —  Thirteen  cases  specially  considered  —  The  effects  of 
crossing  a  self-fertilised  plant  either  by  another  self-fertilised 
plant  or  by  an  intercrossed  plant  of  the  old  stock  —  Summary 
of  the  results  —  Preliminary  remarks  on  the  crossed  and  self- 
fertilised  plants  of  the  same  stock  —  The  twenty-six  exceptional 
cases  considered,  in  which  the  crossed  plants  did  not  exceed 
greatly  in  height  the  self-fertilised  —  Most  of  these  cases  shown 
not  to  be  real  exceptions  to  the  rule  that  cross-fertilisation  is 
beneficial  —  Summary  of  results  —  Relative  weights  of  the 
crossed  and  self-fertilised  plants Page  238-284 


CHAPTER    VIII. 

Difference  between  Crossed  and  Self-fertilised  Plants  in 
Constitutional  Vigour  and  in  other  respects. 

Greater  constitutional  vigour  of  crossed  plants — The  effects  of  great 
crowding  —  Competition  with  other  kinds  of  plants  —  Self-fer- 
tilised plants  more  liable  to  premature  death  —  Crossed  plants 
generally  flower  before  the  self- fertilised  —  Negative  effects  of 
intercrossing  flowers  on  the  same  plant  —  Cases  described  — 
Transmission  of  the  good  effects  of  a  cross  to  later  generations 
—  Effects  of  crossing  plants  of  closely  related  parentage  — 
Uniform  colour  of  the  flowers  on  plants  self-fertilised  during 
several  generations  and  cultivated  under  similar  conditions. 

285-31J 

CHAPTER    IX. 

The  Effects  of  Cross-fertilisation  and  Self-fertilisation 
on  the  Production  of  Seeds. 

Fertility  of  plants  of  crossed  and  self-fertilised  parentage,  both  lots 
being  fertilised  in  the  same  manner  —  Fertility  of  the  parent- 
plants  when  first  crossed  and  self-fertilised,  and  of  their  crossed 


CONTENTS.  Vll 

and  self-fertilised  offspring  when  again  crossed  and  self-fertilised 

—  Comparison  of  the  fertility  of  flowers  fertilised  with  their 
own  pollen  and  with  that  from  other  flowers  on  the  same  plant 

—  Self-sterile  plants  —  Causes  of  self-sterility  —  The  appearance 
of  highly  self-fertile  varieties  —  Self-fertilisation  apparently  in 
some  respects  "beneficial,  independently  of  the  assured  produc- 
tion of  seeds  —  Relative  weights  and  rates  of  germination  of 
seeds  from  crossed  and  self-fertilised  flowers      ..     Page  312-355 


CHAPTEE    X. 

Means  of  Fertilisation. 

Sterility  and  fertility  of  plants  when  insects  are  excluded  —  The 
means  by  which  flowers  are  cross-fertilised  —  Structures  favour- 
able to  self-fertilisation  —  Eelation  between  the  structure  and 
conspicuousness  of  flowers,  the  visits  of  insects,  and  the  advan- 
tages of  cross-fertilisation  —  The  means  by  which  flowers  are 
fertilised  with  pollen  from  a  distinct  plant  —  Greater  fertilising 
power  of  such  pollen  —  Anemophilous  species  —  Conversion  of 
anemophilous  species  into  entomophilous  —  Origin  of  nectar  — 
Anemophilous  plants  generally  have  their  sexes  separated  — 
Conversion  of  diclinous  into  hermaphrodite  flowers  —  Trees 
often  have  their  sexes  separated 356-414 


CHAPTER    XL 

The  Habits  of  Insects  in  relation  to  the  Fertilisation 
of  Flowers. 

Insects  visit  the  flowers  of  the  same  species  as  long  as  they  can  — 
Cause  of  this  habit  —  Means  by  which  bees  recognise  the 
flowers  of  the  same  species  —  Sudden  secretion  of  nectar  — 
Nectar  of  certain  flowers  unattractive  to  certain  insects  —  In- 
dustry of  bees,  and  the  number  of  flowers  visited  within  a  short 
time  —  Perforation  of  the  corolla  by  bees  —  Skill  shown  in  the 
operation  —  Hive-bees  profit  by  the  holes  made  by  humble-bees 
—  Effects  of  habit  —  The  motive  for  perforating  flowers  to  save 
time  —  Flowers  growing  in  crowded  masses  chiefly  perforated. 

415-435 


VU1  CONTENTS. 

CHAPTEE    XII. 

Gekeeal  Eesults. 

Cross-fertilisation  proved  to  be  beneficial,  and  self-fertilisation  in- 
jurious—  Allied  species  differ  greatly  in  the  means  by  which 
cross-fertilisation  is  favoured  and  self-fertilisation  avoided  — 
The  benefits  and  evils  of  the  two  processes  depend  on  the  degree 
of  differentiation  in  the  sexual  elements  —  The  evil  effects  not 
due  to  the  combination  of  morbid  tendencies  in  the  parents  — 
Nature  of  the  conditions  to  which  plants  are  subjected  when 
growing  near  together  in  a  state  of  nature  or  under  culture,  and 
the  effects  of  such  conditions  —  Theoretical  considerations  with 
respect  to  the  interaction  of  differentiated  sexual  elements  — 
Practical  lessons  —  Genesis  of  the  two  sexes  —  Close  correspon- 
dence between  the  effects  of  cross-fertilisation  and  self-fertilisa- 
tion, and  of  the  legitimate  and  illegitimate  unions  of  hetero- 
styled  plants,  in  comparison  with  hybrid  unions    Page  436-469 


Indbx Page  471—482 


THE 

EFFECTS 

OF 

CEOSS  AND  SELF-FEKTILISATION. 


CHAPTER  I. 

INTRODUCTORY   KeHARKS. 

Various  means  which  favour  or  determine  the  cross -fertilisation  of 
plants — Benefits  derived  from  cross-fertilisation — Self-fertilisation 
favourable  to  the  propagation  of  the  species — Brief  history  of  the 
subject — Object  of  the  experiments,  and  the  manner  in  which  they 
were  tried — Statistical  value  of  the  measurements — The  experi- 
ments carried  on  during  several  successive  generations — Nature 
of  the  relationship  of  the  plants  in  the  later  generations — Unifor- 
mity of  the  conditions  to  which  the  plants  were  subjected — Some 
apparent  and  some  real  causes  of  error — Amount  of  pollen  em- 
ployed— Arrangement  of  the  work — Importance  of  the  conclusions. 

Theee  is  weighty  and  abundant  evidence  that  the 
flowers  of  most  kinds  of  plants  are  constructed  so  as 
to  be  occasionally  or  habitually  cross-fertilised  by 
pollen  from  another  flower,  produced  either  by  the 
same  plant,  or  generally,  as  we  shall  hereafter  see 
reason  to  believe,  by  a  distinct  plant.  Cross-fertilisa- 
tion is  sometimes  ensured  by  the  sexes  being  separated, 
and  in  a  large  number  of  cases  by  the  pollen  and 
stigma  of  the  same  flower  being  matured  at  different 
times.  Such  plants  are  called  dichogamous,  and  have 
been  divided  into  two  sub-classes :  proterandrous  species, 


2  INTRODUCTORY  REMARKS.  Chap.  I. 

in  which  the  pollen  is  mature  before  the  stigma,  and 
proterogynous  species,  in  which  the  reverse  occurs ; 
this  latter  form  of  dichogamy  not  being  nearly  so 
common  as  the  other.  Cross-fertilisation  is  also  en- 
sured, in  many  cases,  by  mechanical  contrivances  of 
wonderful  beauty,  preventing  the  impregnation  of  the 
flowers  by  their  own  pollen.  There  is  a  small  class  of 
plants,  which  I  have  called  dimorphic  and  trimorphic, 
but  to  which  Hildebrand  has  given  the  more  appro- 
priate name  of  heterostyled ;  this  class  consists  of 
plants  presenting  two  or  three  distinct  forms,  adapted 
for  reciprocal  fertilisation,  so  that,  like  plants  with 
separate  sexes,  they  can  hardly  fail  to  be  intercrossed 
in  each  generation.  The  male  and  female  organs  of 
some  flowers  are  irritable,  and  the  insects  which  touch 
them  get  dusted  with  pollen,  which  is  thus  transported 
to  other  flowers.  Again,  there  is  a  class,  in  which  the 
ovules  absolutely  refuse  to  be  fertilised  by  pollen  from 
the  same  plant,  but  can  be  fertilised  by  pollen  from 
any  other  individual  of  the  same  species.  There  are 
also  very  many  species  which  are  partially  sterile  with 
their  own  pollen.  Lastly,  there  is  a  large  class  in 
which  the  flowers  present  no  apparent  obstacle  of  any 
kind  to  self-fertilisation,  nevertheless  these  plants  are 
frequently  intercrossed,  owing  to  the  prepotency  of 
pollen  from  another  individual  or  variety  over  the 
plant's  own  pollen. 

As  plants  are  adapted  by  such  diversified  and  effec- 
tive means  for  cross-fertilisation,  it  might  have  been 
inferred  from  this  fact  alone  that  they  derived  some 
great  advantage  from  the  process  ;  and  it  is  the  object 
of  the  present  work  to  show  the  nature  and  importance 
of  the  benefits  thus  derived.  There  are,  however,  some 
exceptions  to  the  rule  of  plants  being  constructed  so 
as  to  allow  of  or  to  favour  cross-fertilisation,  for  some 


Chap.  I.  INTRODUCTORY   REMARKS.  3 

few  plants  seem  to  be  invariably  self-fertilised;  yet 
even  these  retain  traces  of  having  been  formerly 
adapted  for  cross-fertilisation.  These  exceptions  need 
not  make  us  doubt  the  truth  of  the  above  rule,  any 
more  than  the  existence  of  some  few  plants  which  pro- 
duce flowers,  and  yet  never  set  seed,  should  make  us 
doubt  that  flowers  are  adapted  for  the  production  of 
seed  and  the  propagation  of  the  species. 

We  should  always  keep  in  mind  the  obvious  fact 
that  the  production  of  seed  is  the  chief  end  of  the 
act  of  fertilisation ;  and  that  this  end  can  be  gained 
by  hermaphrodite  plants  with  incomparably  greater 
certainty  by  self-fertilisation,  than  by  the  union  of 
the  sexual  elements  belonging  to  two  distinct  flowers 
or  plants.  Yet  it  is  as  unmistakably  plain  that  innu- 
merable flowers  are  adapted  for  cross-fertilisation,  as 
that  the  teeth  and  talons  of  a  carnivorous  animal  are 
adapted  for  catching  prey  ;  or  that  the  plumes,  wings, 
and  hooks  of  a  seed  are  adapted  for  its  dissemination. 
Flowers,  therefore,  are  constructed  so  as  to  gain  two 
objects  which  are,  to  a  certain  extent,  antagonistic,  and 
this  explains  many  apparent  anomalies  in  their  struc- 
ture. The  close  proximity  of  the  anthers  to  the  stigma 
in  a  multitude  of  species  favours,  and  often  leads,  to 
self-fertilisation ;  but  this  end  could  have  been  gained 
far  more  safely  if  the  flowers  had  been  completely 
closed,  for  then  the  pollen  would  not  have  been  injured 
by  the  rain  or  devoured  by  insects,  as  often  happens. 
Moreover,  in  this  case,  a  very  small  quantity  of  pollen 
would  have  been  sufficient  for  fertilisation,  instead  of 
millions  of  grains  being  produced.  But  the  openness 
of  the  flower  and  the  production  of  a  great  and  ap- 
parently wasteful  amount  of  pollen  are  necessary  for 
cross-fertilisation.  These  remarks  are  well  illustrated 
by  the  plants  called  cleistogene,  which  bear  on  the 


4  INTEODUCTOET  EEMAEKS.  Chap.  I. 

same  stock  two  kinds  of  flowers.  The  flowers  of  trie  one 
kind  are  minute  and  completely  closed,  so  that  they 
cannot  possibly  be  crossed ;  but  they  are  abundantly 
fertile,  although  producing  an  extremely  small 
quantity  of  pollen.  The  flowers  of  the  other  kind 
produce  much  pollen  and  are  open ;  and  these  can  be, 
and  often  are,  cross-fertilised.  Hermann  Miiller  has 
also  made  the  remarkable  discovery  that  there  are 
some  plants  which  exist  under  two  forms ;  that  is, 
produce  on  distinct  stocks  two  kinds  of  hermaphrodite 
flowers.  The  one  form  bears  small  flowers  constructed 
for  self-fertilisation  ;  whilst  the  other  bears  larger  and 
much  more  conspicuous  flowers  plainly  constructed 
for  cross-fertilisation  by  the  aid  of  insects ;  and  without 
their  aid  these  produce  no  seed. 

The  adaptation  of  flowers  for  cross-fertilisation  is  a 
subject  which  has  interested  me  for  the  last  thirty- 
seven  years,  and  I  have  collected  a  large  mass  of  ob- 
servations, but  these  are  now  rendered  superfluous  by 
the  many  excellent  works  which  have  been  lately  pub- 
lished. In  the  year  1857  I  wrote  *  a  short  paper  on 
the  fertilisation  of  the  kidney  bean ;  and  in  1862  my 
work  '  On  the  Contrivances  by  which  British  and 
Foreign  Orchids  are  Fertilised  by  Insects '  appeared. 
It  seemed  to  me  a  better  plan  to  work  out  one  group 
of  plants  as  carefully  as  I  could,  rather  than  to  pub- 
lish many  miscellaneous  and  imperfect  observations. 
My  present  work  is  the  complement  of  that  on 
Orchids,  in  which  it  was  shown  how  admirably  these 
plants  are  constructed  so  as  to  permit  of,  or  to  favour, 
or  to  necessitate  cross-fertilisation.     The  adaptations 


*  '  Gardeners'  Chronicle,'  1 857,      *  Annals  and  Mag.  of  Nat.  Hist, 
p.  725,  and  1858,  pp.  824  and  844.       3rd  series,  vol.  ii.  1858,  p.  462. 


Chap.  I.  INTRODUCTORY   REMARKS.  5 

for  cross-fertilisation  are  perhaps  more  obvious  m  the 
Orchidese  than  in  any  other  group  of  plants,  but  it  is 
an  error  to  speak  of  them,  as  some  authors  have  done, 
as  an  exceptional  case.  The  lever-like  action  of  the 
stamens  of  Salvia  (described  by  Hildebrand,  Dr.  W. 
Ogle,  and  others),  by  which  the  anthers  are  depressed 
and  rubbed  on  the  backs  of  bees,  shows  as  perfect  a 
structure  as  can  be  found  in  any  orchid.  Papilion- 
aceous flowers,  as  described  by  various  authors — for 
instance,  by  Mr.  T.  H.  Farrer — offer  innumerable 
curious  adaptations  for  cross-fertilisation.  The  case  of 
Posoqueria  fragrans  (one  of  the  Rubiacea;),  is  as  won- 
derful as  that  of  the  most  wonderful  orchid.  The 
stamens,  according  to  Fritz  Miiller,*  are  irritable,  so 
that  as  soon  as  a  moth  visits  a  flower,  the  anthers  ex- 
plode and  cover  the  insect  with  pollen ;  one  of  the 
filaments  which  is  broader  than  the  others  then  moves 
and  closes  the  flower  for  about  twelve  hours,  after 
which  time  it  resumes  its  original  position.  Thus  the 
stigma  cannot  be  fertilised  by  pollen  from  the  same 
flower,  but  only  by  that  brought  by  a  moth  from  some 
other  flower.  Endless  other  beautiful  contrivances  for 
this  same  purpose  could  be  specified. 

Long  before  I  had  attended  to  the  fertilisation  of 
flowers,  a  remarkable  book  appeared  in  1793  in  Ger- 
many, 'Das  Entdeckte  Geheimniss  der  Natur,'  by 
C.  K.  Sprengel,  in  which  he  clearly  proved  by  innumer- 
able observations,  how  essential  a  part  insects  play  in 
the  fertilisation  of  many  plants.  But  he  was  in  ad- 
vance of  his  age,  and  his  discoveries  were  for  a  long 
time  neglected.  Since  the  appearance  of  my  book  on 
Orchids,  many  excellent  works  on  the  fertilisation  of 
flowers,  such  as  those  by  Hildebrand,  Delpino,  Axell. 


*  '  Botanische  Zeitung,'  186(3,  p.  129. 


6  INTEODUCTOEY  EEMAEKS.  Cbap.  I. 

and  Hermann  Miiller,*  and  numerous  shorter  papers, 
have  been  published.  A  list  would  occupy  several 
pages,  and  this  is  not  the  proper  place  to  give  their 
titles,  as  we  are  not  here  concerned  with  the  means, 
but  with  the  results  of  cross-fertilisation.  No  one 
who  feels  interest  in  the  mechanism  by  which  nature 
effects  her  ends,  can  read  these  books  and  memoirs 
without  the  most  lively  interest. 

From  my  own  observations  on  plants,  guided  to  a 
certain  extent  by  the  experience  of  the  breeders  of 
animals,  I  became  convinced  many  years  ago  that  it 
is  a  general  law  of  nature  that  flowers  are  adapted  to 
be  crossed,  at  least  occasionally,  by  pollen  from  a 
distinct  plant.  Sprengel  at  times  foresaw  this  law,  but 
only  partially,  for  it  does  not  aj)pear  that  he  was  aware 
that  there  was  any  difference  in  power  between  pollen 
from  the  same  plant  and  from  a  distinct  plant.  In  the 
introduction  to  his  book  (p.  4)  he  says,  as  the  sexes 
are  separated  in  so  many  flowers,  and  as  so  many  other 
flowers  are  dichogamous,  "  it  appears  that  nature  has 
not  willed  that  any  one  flower  should  be  fertilised  by 
its  own  pollen."  Nevertheless,  he  was  far  from  keeping 
this  conclusion  always  before  his  mind,  or  he  did  not 


*  Sir  John  Lubbock  bas  given  known,  visit  the  flowers  of  each 

an   interesting    summary   of   the  species.     He   likewise    enters   on 

whole  subject  in  his  '  British  Wild  new  ground,  by  showing  not  only 

Flowers  considered  in  relation  to  that  flowers  arc  adapted  for  their 

Insects,'  1875.     Hermann  Muller's  own  good  to  the  visits  of  certain 

work  '  Die  Befruchtung  der  Biu-  insects  ;    but   that    the    insects 

men  durch  Insekten,'  1873,  con-  themselves  are  excellently  adapted 

tains    an    immense    number     of  for   procuring   nectar    or   pollen 

original    observations    and    gene-  from  certain  flowers.     The  value 

ralisations.     It   is,  moreover,    in-  of  H.  Muller's  work  can  hardly  be 

valuable  as  a  repertory  with  re-  over-estimated,  and  it  is  much  to 

ferences     to    almost    everything  be  desired  that  it  should  be  trans- 

whieh  has  been  published  on  the  lated     into      English.      Severin 

subject.     His   work    differs  from  Axell's  work  is  written  in  Swedish, 

that   of  all  others  in   specifying  so  that  I  have  not  been  able  to 

what  kinds  of  insects,  as  far  as  read  it. 


Chap.  I.  INTRODUCTORY  REMARKS.  7 

see  its  full  importance,  as  may  be  perceived  by  any- 
one who  will  read  his  observations  carefully  ;  and  he 
consequently  mistook  the  meaning  of  various  struc- 
tures. But  his  discoveries  are  so  numerous  and  his 
work  so  excellent,  that  he  can  well  afford  to  bear  a 
small  amount  of  blame.  A  most  capable  judge,  H. 
Miiller,  likewise  says  :*  "  It  is  remarkable  in  how  very 
many  cases  Sprengel  rightly  perceived  that  pollen  is 
necessarily  transported  to  the  stigmas  of  other  flowers 
of  the  same  species  by  the  insects  which  visit  them, 
and  yet  did  not  imagine  that  this  transportation  was 
of  any  service  to  the  plants  themselves." 

Andrew  Knight  saw  the  truth  much  more  clearly, 
for  he  remarks,!  "  Nature  intended  that  a  sexual  in- 
tercourse should  take  place  between  neighbouring 
plants  of  the  same  species."  After  alluding  to  the 
various  means  by  which  pollen  is  transported  from 
flower  to  flower,  as  far  as  was  then  imperfectly  known, 
he  adds,  "  Nature  has  something  more  in  view  than  that 
its  own  proper  males  should  fecundate  each  blossom." 
In  1811  Kolreuter  plainly  hinted  at  the  same  law,  as 
did  afterwards  another  famous  hybridiser  of  plants, 
Herbert.^  But  none  of  these  distinguished  observers 
appear  to  have  been  sufficiently  impressed  with  the 


*  'Die  Befruchtung  der  Blu-  %  Kolreuter,  '  Mem.  de  l'Aead. 

men,'  1873,  p.  4.     His  words  are:  de  St.  Petersbourg,'  torn.  iii.  18)9 

"  Es  ist  merkwiirdig,  in  wie  zahl-  (published  1811),  p.  197.     After 

reichen   Fallen   Sprengel  richtig  showing  how  well  the  Malvaceso 

erkannte,  dass  durch  die  Besuoh-  are,  adapted  for  cross-fertilisation, 

enden  Insekten  der  Bliithenstaub  he  asks,  "  An  id  aliquid  in  reces-su 

mit  Nothwendigkeit  auf  die  Nar-  habeat,  quod  hujuscemodi   floies 

ben    anderer    Bliithen    derselhen  nunquam  proprio  suo  pulvere,  sed 

Art  iibertragen  wird,  ohne  auf  die  semper    eo   aliarum  suss   speciei 

Vermuthung  zu  kommen,  dass  in  impregnentur,   merito    quseritur? 

dieser  Wirkung  der  Nutzen  des  Certe  natura  nil    facit    frustra." 

Insektenbesuch.es  fur  die  Pfianzen  Herbert,  '  Aniaryllidaceae,  with  a 

selbst  gesucht  werden  miisse."  Treatise    on     Cross-bred     Yege- 

t  '  Philosophical  Transactions,'  tables,'  1837. 
1799,  p.  202. 


8  INTRODUCTORY  REMARKS.  Chap.  I 

truth  and  generality  of  the  law,  so  as  to  insist  on  it 
and  impress  their  belief  on  others. 

In  1862  I  summed  up  my  observations  on  Orchids 
by  saying  that  nature  "  abhors  perpetual  self-fertilisa- 
tion." If  the  word  perpetual  had  been  omitted,  the 
aphorism  would  have  been  false.  As  it  stands,  I 
believe  that  it  is  true,  though  perhaps  rather  too 
strongly  expressed ;  and  I  should  have  added  the 
self-evident  proposition  that  the  propagation  of  the 
species,  whether  by  self-fertilisation  or  by  cross-fertili- 
sation, or  asexually  by  buds,  stolons,  &c.  is  of  paramount 
importance.  Hermann  Miiller  has  done  excellent 
service  by  insisting  repeatedly  on  this  latter  point. 

It  often  occurred  to  me  that  it  would  be  advisable 
to  try  whether  seedlings  from  cross-fertilised  flowers 
were  in  any  way  superior  to  those  from  self-fertilised 
flowers.  But  as  no  instance  was  known  with  animals 
of  any  evil  appearing  in  a  single  generation  from  the 
closest  possible  interbreeding,  that  is  between  brothers 
and  sisters,  I  thought  that  the  same  rule  would  hold 
good  with  plants ;  and  that  it  would  be  necessary  at 
the  sacrifice  of  too  much  time  to  self-fertilise  and  inter- 
cross plants  during  several  successive  generations,  in 
order  to  arrive  at  any  result.  I  ought  to  have  re- 
flected that  such  elaborate  provisions  favouring  cross- 
fertilisation,  as  we  see  in  innumerable  plants,  would 
not  have  been  acquired  for  the  sake  of  gaining  a 
distant  and  slight  advantage,  or  of  avoiding  a  distant 
and  slight  evil.  Moreover,  the  fertilisation  of  a  flower 
by  its  own  pollen  corresponds  to  a  closer  form  of  inter- 
breeding than  is  possible  with  ordinary  bi-sexual 
animals;  so  that  an  earlier  result  might  have  been 
expected. 

I  was  at  last  led  to  make  the  experiments  recorded 
in  the  present  volume  from  the  following  circumstance. 


Chap.  I.  INTRODUCTORY  REMARKS.  9 

For  the  sake  of  determining  certain  points  with,  respect 
to  inheritance,  and  without  any  thought  of  the  effects 
of  close  interbreeding,  I  raised  close  together  two 
large  beds  of  self-fertilised  and  crossed  seedlings  from 
the  same  plant  of  Linaria  vulgaris.  To  my  surprise, 
the  crossed  plants  when  fully  grown  were  plainly  taller 
and  more  vigorous  than  the  self-fertilised  ones.  Bees 
incessantly  visit  the  flowers  of  this  Linaria  and  carry 
pollen  from  one  to  the  other ;  and  if  insects  are  ex- 
cluded, the  flowers  produce  extremely  few  seeds ;  so 
that  the  wild  plants  from  which  my  seedlings  were 
raised  must  have  been  intercrossed  during  all  previous 
generations.  It  seemed  therefore  quite  incredible  that 
the  difference  between  the  two  beds  of  seedlings  could 
have  been  due  to  a  single  act  of  self-fertilisation  ;  and 
I  attributed  the  result  to  the  self-fertilised  seeds  not 
having  been  well  ripened,  improbable  as  it  was  that  all 
should  have  been  in  this  state,  or  to  some  other 
accidental  and  inexplicable  cause.  During  the  next 
year,  I  raised  for  the  same  purpose  as  before  two  large 
beds  close  together  of  self-fertilised  and  crossed  seed- 
lings from  the  carnation,  Dianthus  caryophyllus.  This 
plant,  like  the  Linaria,  is  almost  sterile  if  insects  are 
excluded ;  and  we  may  draw  the  same  inference  as 
before,  namely,  that  the  parent-plants  must  have  been 
intercrossed  during  every  or  almost  every  previous 
generation.  Nevertheless,  the  self-fertilised  seedlings 
were  plainly  inferior  in  height  and  vigour  to  the 
crossed. 

My  attention  was  now  thoroughly  aroused,  for  I  could 
hardly  doubt  that  the  difference  between  the  two  beds 
was  due  to  the  one  set  being  the  offspring  of  crossed, 
and  the  other  of  self-fertilised  flowers.  Accordingly  I 
selected  almost  by  hazard  two  other  plants,  which 
happened  to  be  in  flower  in  the  greenhouse,  namely, 


10  INTKODUCTOKY  KE1HAEKS.  Chaf.  I. 

Mimulus  luteus  and  Ipomoea  purpurea,  both  of  which, 
unlike  the  Linaria  and  Dianthus,  are  highly  self- 
fertile  if  insects  are  excluded.  Some  flowers  on  a 
single  plant  of  both  species  were  fertilised  with  their 
own  pollen,  and  others  were  crossed  with  pollen  from 
a  distinct  individual ;  both  plants  being  protected  by  a 
net -from  insects.  The  crossed  and  self-fertilised  seeds 
thus  produced  were  sown  on  opposite  sides  of  the  same 
pots,  and  treated  in  all  respects  alike ;  and  the  plants 
when  fully  grown  were  measured  and  compared.  With 
both  species,  as  in  the  cases  of  the  Linaria  and 
Dianthus,  the  crossed  seedlings  were  conspicuously 
superior  in  height  and  in  other  ways  to  the  self- 
fertilised.  I  therefore  determined  to  begin  a  long 
series  of  experiments  with  various  plants,  and  these 
were  continued  for  the  following  eleven  years ;  and  we 
shall  see  that  in  a  large  majority  of  cases  the  crossed 
beat  the  self-fertilised  plants.  Several  of  the  excep- 
tional cases,  moreover,  in  which  the  crossed  plants 
were  not  victorious,  can  be  explained. 

It  should  be  observed  that  I  have  spoken  for  the 
sake  of  brevity,  and  shall  continue  to  do  so,  of  crossed 
and  self-fertilised  seeds,  seedlings,  or  plants;  these 
terms  implying  that  they  are  the  product  of  crossed  or 
self-fertilised  flowers.  Cross-fertilisation  always  means 
a  cross  between  distinct  plants  which  were  raised  from 
seeds  and  not  from  cuttings  or  buds.  Self -fertilisation 
always  implies  that  the  flowers  in  question  were  im- 
pregnated with  their  own  pollen. 

My  experiments  were  tried  in  the  following  manner. 
A  single  plant,  if  it  produced  a  sufficiency  of  flowers,  or 
two  or  three  plants  were  placed  under  a  net  stretched 
on  a  frame,  and  large  enough  to  cover  the  plant 
(together  with  the  pot,  when  one  was  used)  without 
touching    it.     This  latter  point  is  important,  for    if 


Ohap.  I.  INTRODUCTORY   REMARKS.  11 

the  flowers  touch  the  net  they  may  be  cross-fertilised 
by  bees,  as  I  have  known  to  happen ;  and  when  the  net 
is  wet  the  pollen  may  be  injured.  I  used  at  first 
"  white  cotton  net,"  with  very  fine  meshes,  but  after- 
wards a  kind  of  net  with  meshes  one-tenth  of  an 
inch  in  diameter;  and  this  I  found  by  experience 
effectually  excluded  all  insects  excepting  Thrips,  which 
no  net  will  exclude.  On  the  plants  thus  protected 
several  flowers  were  marked,  and  were  fertilised  with 
their  own  pollen ;  and  an  equal  number  on  the  same 
plants,  marked  in  a  different  manner,  were  at  the  same 
time  crossed  with  pollen  from  a  distinct  plant.  The 
crossed  flowers  were  never  castrated,  in  order  to  make 
the  experiments  as  like  as  possible  to  what  occurs 
under  nature  with  plants  fertilised  by  the  aid  of 
insects.  Therefore,  some  of  the  flowers  which  were 
crossed  may  have  failed  to  be  thus  fertilised,  and 
afterwards  have  been  self-fertilised.  But  this  and 
some  other  sources  of  error  will  presently  be  discussed. 
In  some  few  cases  of  spontaneously  self-fertile  species, 
the  flowers  were  allowed  to  fertilise  themselves  under 
the  net ;  and  in  still  fewer  cases  uncovered  plants  were 
allowed  to  be  freely  crossed  by  the  insects  which  in- 
cessantly visited  them.  There  are  some  great  advan- 
tages and  some  disadvantages  in  my  having  occasion- 
ally varied  my  method  of  proceeding ;  but  when  there 
was  any  difference  in  the  treatment,  it  is  always  so 
stated  under  the  head  of  each  species. 

Care  was  taken  that  the  seeds  were  thoroughly 
ripened  before  being  gathered.  Afterwards  the  crossed 
and  self-fertilised  seeds  were  in  most  cases  placed  on 
damp  sand  on  opposite  sides  of  a  glass  tumbler  covered 
by  a  glass  plate,  with  a  partition  between  the  two  lots  ; 
and  the  glass  was  placed  on  the  chimney-piece  in  a 
warm  room.     I  could  thus  observe  the  germination  of 


12  INTRODUCTORY  REMARKS.  Chap.  L 

the  seeds.  Sometimes  a  few  would  germinate  on  one 
side  before  any  on  the  other,  and  these  were  thrown 
away.  But  as  often  as  a  pair  germinated  at  the  same 
time,  they  were  planted  on  opposite  sides  of  a  pot,  with 
a  superficial  partition  between  the  two;  and  I  thus 
proceeded  until  from  half-a-dozen  to  a  score  or  more 
seedlings  of  exactly  the  same  age  were  planted  on 
the  opposite  sides  of  several  pots.  If  one  of  the  young 
seedlings  became  sickly  or  was  in  any  way  injured, 
it  was  pulled  up  and  thrown  away,  as  well  as  its 
antagonist  on  the  opposite  side  of  the  same  pot. 

As  a  large  number  of  seeds  were  placed  on  the  sand 
to  germinate,  many  remained  after  the  pairs  had  been 
selected,  some  of  which  were  in  a  state  of  germination 
and  others  not  so ;  and  these  were  sown  crowded 
together  on  the  opposite  sides  of  one  or  two  rather 
larger  pots,  or  sometimes  in  two  long  rows  out  of  doors. 
In  these  cases  there  was  the  most  severe  struggle  for 
life  among  the  crossed  seedlings  on  one  side  of  the 
pot,  and  the  self-fertilised  seedlings  on  the  other  side, 
and  between  the  two  lots  which  grew  in  competition 
in  the  same  pot.  A  vast  number  soon  perished, 
and  the  tallest  of  the  survivors  on  both  sides  when 
fully  grown  were  measured.  Plants  treated  in  this 
manner,  were  subjected  to  nearly  the  same  conditions 
as  those  growing  in  a  state  of  nature,  which  have  to 
struggle  to  maturity  in  the  midst  of  a  host  of 
competitors. 

On  other  occasions,  from  the  want  of  time,  the  seeds, 
instead  of  being  allowed  to  germinate  on  damp  sand, 
were  sown  on  the  opposite  sides  of  pots,  and  the  fully 
grown  plants  measured.  But  this  plan  is  less  accurate, 
as  the  seeds  sometimes  germinated  more  quickly  on 
one  side  than  on  the  other.  It  was  however  necessary 
to  act  in  this  manner  with  some  few  species,  as  certain 


Chap.:..  INTRODUCTORY   REMARKS.  13 

kinds  of  seeds  would  not  germinate  well  when  exposed 
to  the  light ;  though  the  glasses  containing  them  were 
kept  on  the  chimney-piece  on  one  side  of  a  room, 
and  some  way  from  the  two  windows  which  faced 
the  N.E.* 

The  soil  in  the  pots  in  which  the  seedlings  were 
planted,  or  the  seeds  sown,  was  well  mixed,  so  as  to 
be  uniform  in  composition.  The  plants  on  the  two 
sides  were  always  watered  at  the  same  time  and  as 
equally  as  possible ;  and  even  if  this  had  not  been 
done,  the  water  would  have  spread  almost  equally  to 
both  sides,  as  the  pots  were  not  large.  The  crossed 
and  self-fertilised  plants  were  separated  by  a  super- 
ficial partition,  which  was  always  kept  directed  towards 
the  chief  source  of  the  light,  so  that  the  plants  on  both 
sides  were  equally  illuminated.  I  do  not  believe  it 
possible  that  two  sets  of  plants  could  have  been  sub- 
jected to  more  closely  similar  conditions,  than  were 
my  crossed  and  self-fertilised  seedlings,  as  grown  in 
the  above  described  manner. 

In  comparing  the  two  sets,  the  eye  alone  was  never 
trusted.  Generally  the  height  of  every  plant  on  both 
sides  was  carefully  measured,  often  more  than  once, 
viz.,  whilst  young,  sometimes  again  when  older,  and 
finally  when  fully  or  almost  fully  grown.  But  in 
some  cases,  which  are  always  specified,  owing  to  the 
want  of  time,  only  one  or  two  of  the  tallest  plants  on 
each  side  were  measured.  This  plan,  which  is  not  a 
good  one,  was  never  followed  (except  with  the  crowded 


*  This  occurred  in  the  plainest  species  germinated  on  the  bare 

manner  with  the  seeds  of  Papaver  sand,  thuugh  left  there  for  some 

vagum  and  Delphinium  consolida,  weeks ;'  but  when  these  same  seeds 

and  less   plainly   with  those    of  were  placed  on  earth  in  pots,  and 

Adonis  aestivalis  and  Ononis minu-  covered  with  a  thiu  layer  of  sand, 

tissima.     Rarely  more  than  one  they  germinated  immediately  in 

or  two  of  the  seeds  of  these  four  large  numbers. 


14  INTEODUCTOEY   EEMAEKS.  Chap.  I 

plants  raised  from  the  seeds  remaining  after  the  pairs 
had  been  planted)  unless  the  tallest  plants  on  each 
side  seemed  fairly  to  represent  the  average  difference 
between  those  on  both  sides.  It  has,  however,  some 
great  advantages,  as  sickly  or  accidentally  injured 
plants,  or  the  offspring  of  ill-ripened  seeds,  are  thus 
eliminated.  When  the  tallest  plants  alone  on  each  side 
were  measured,  their  average  height  of  course  exceeds 
that  of  all  the  plants  on  the  same  side  taken  together. 
But  in  the  case  of  the  much  crowded  plants  raised 
from  the  remaining  seeds,  the  average  height  of  the 
tallest  plants  was  less  than  that  of  the  plants  in  pairs, 
owing  to  the  unfavourable  conditions  to  which  they 
were  subjected  from  being  greatly  crowded.  For  our 
purpose,  however,  of  the  comparison  of  the  crossed  and 
self-fertilised  plants,  their  absolute  height  signifies 
little. 

As  the  plants  were  measured  by  an  ordinary  English 
standard  divided  into  inches  and  eighths  of  an  inch,  I 
have  not  thought  it  worth  while  to  change  the  frac- 
tions into  decimals.  The  average  or  mean  heights 
were  calculated  in  the  ordinary  rough  method  by 
adding  up  the  measurements  of  all,  and  dividing  the 
product  by  the  number  of  plants  measured ;  the  result 
being  here  given  in  inches  and  decimals.  As  the 
different  species  grow  to  various  heights,  I  have  always 
for  the  sake  of  easy  comparison  given  in  addition  the 
average  height  of  the  crossed  plants  of  each  species 
taken  as  100,  and  have  calculated  the  average  height 
of  the  self-fertilised  plant  in  relation  to  this  standard. 
With  respect  to  the  crowded  plants  raised  from  the 
seeds  remaining  after  the  pairs  had  been  planted, 
and  of  which  only  some  of  the  tallest  on  each  side 
were  measured,  I  have  not  thought  it  worth  while  to 
complicate  the  results  by  giving   separate  averages 


Chap.  I.  INTRODUCTOEY  REMARKS.  15 

for  them  and  for  the  pairs,  but  have  added  up  all 
their  heights,  and  thus  obtained  a  single  average. 

I  long  doubted  whether  it  was  worth  while  to  give 
the  measurements  of  each  separate  plant,  but  have 
decided  to  do  so,  in  order  that  it  may  be  seen  that  the 
superiority  of  the  crossed  plants  over  the  self-fertilised, 
does  not  commonly  depend  on  the  presence  of  two  or 
three  extra  fine  plants  on  the  one  side,  or  of  a  few 
very  poor  plants  on  the  other  side.  Although  several 
observers  have  insisted  in  general  terms  on  the  off- 
spring from  intercrossed  varieties  being  superior  to 
either  parent-form,  no  precise  measurements  have  been 
given  ;*  and  I  have  met  with  no  observations  on 
the  effects  of  crossing  and  self-fertilising  the  indi- 
viduals of  the  same  variety.  Moreover,  experiments  of 
this  kind  require  so  much  time — mine  having  been 
continued  during  eleven  years — that  they  are  not 
likely  soon  to  be  repeated. 

As  only  a  moderate  number  of  crossed  and  self- 
fertilised  plants  were  measured,  it  was  of  great  impor- 
tance to  me  to  learn  how  far  the  averages  were  trust- 
worthy. I  therefore  asked  Mr.  Galton,  who  has  had 
much  experience  in  statistical  researches,  to  examine 
some  of  my  tables  of  measurements,  seven  in  number, 
namely,  those  of  Ipomoea,  Digitalis,  Beseda  lutea, 
Viola,  Limnanthes,  Petunia,  and  Zea.  I  may  premise 
that  if  we  took  by  chance  a  dozen  or  score  of  men 
belonging  to  two  nations  and  measured  them,  it  would 
I  presume  be  very  rash  to  form  any  judgment  from 
such  small  numbers  on  their  average  heights.  But 
the  case  is  somewhat  different  with  my  crossed  and 
self-fertilised  plants,  as  they  were  of  exactly  the  same 


*  A  summary  of  these  state-  and  Plants  under  Domestication, 

ments,   with   references,  may  be  chap,  xvii.,   2nd  edit.,  1875,  vol 

found  in  my  '  Variation  of  Animals  ii.  p.  109. 

2 


16 


INTRODUCTORY   KEMAEKS. 


Ohaf.  L 


age,  were  subjected  from  first  to  last  to  tfie  same 
conditions,  and  were  descended  from  the  same  parents. 
When  only  from  two  to  six  pairs  of  plants  were 
measured,  the  results  are  manifestly  of  little  or  no 
value,  except  in  so  far  as  they  confirm  and  are  con- 
firmed by  experiments  made  on  a  larger  scale  with 
other  species.  I  will  now  give  the  report  on  the  seven 
tables  of  measurements,  which  Mr.  Galton  has  had  the 
great  kindness  to  draw  up  for  me. 

"  I  have  examined  the  measurements  of  the  plants  with  care, 
and  by  many  statistical  methods,  to  find  ont  how  far  the  means 
of  the  several  sets  represent  constant  realities,  such  as  would 
come  out  the  same  so  long  as  the  general  conditions  of  growth 
remained  unaltered.  The  principal  methods  that  were  adopted 
are  easily  explained  by  selecting  one  of  the  shorter  series 
of  plants,  say  of  Zea  mays,  for  an  example." 

Zea  mays  (young  plants'). 


Arranged  » 

Order  of  Magnitude. 

As  recorded  by  Mr.  Darwin. 

In  Separate  Pots. 

In 

i  Single  Series. 

Column  I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

Crossed. 

Self-fert. 

Crossed. 

Self-fert. 

Crossed. 

Self-fert. 

Difference 

Inches. 

Inches. 

Inches. 

Inches. 

Inches. 

Inches. 

Inches. 

23 1 

171 

23 1 

20| 

23f 

20| 

-31 

Pot  I. 

12 

2.0 1 

21 

20 

231 

20 

-31 

21 

20 

12 

171 

23 

22  i 

20 
18f 

-3 

22 

20 

22 

20 

22i 

18f 

—  3* 

Pot  II. 

19 1 

18f 

211 

18| 

22 

181 

—  35 

21| 

18| 

19 1 

181 

21 1 

214 

18 

18 

—  S3 

—  °s 
~3| 

22 | 

18 1 

23f 

18f 

21 

18 

-3 

20 1 

15f 

22 1 

18 

21 

171 

-3| 

Pot  III. 

18§ 

16  j 

21| 

16| 

201 

16| 

-31 

21 1 

18 

20  i 

16§ 

19.1 

16f 

-21 

23§ 

161 

18§ 

15§ 

181 
12 

151 
15f 

-21 

+31 

21 

18 

23 

18 

12 

12f 

+og 

Pot  IV. 

22$ 

12| 

22  i 

18 

23 

15 1 

21 

15  J 

12 

18 

12 

12| 

Chap.  I. 


INTRODUCTORY    REMARKS. 


"  The  observations  as  I  received  them  are  shown  in  columns  II. 
and  III.,  where  they  certainly  have  no  prima  facie  appearance  of 
regularity.  But  as  soon  as  we  arrange  them  in  the  order  of 
their  magnitudes,  as  in  columns  IV.  and  V.,  the  case  is  materially 
altered.  We  now  see,  with  few  exceptions,  that  the  largest 
plant  on  the  crossed  side  in  each  pot  exceeds  the  largest  plant 
on  the  self-fertilised  side,  that  the  second  exceeds  the  second, 
the  third  the  third,  and  so  on.  Out  of  the  fifteen  cases  in  the 
table,  there  are  only  two  exceptions  to  this  rule.  We  may 
therefore  confidently  affirm  that  a  crossed  series  will  always 
be  found  to  exceed  a  self-fertilised  series,  within  the  range  of 
the  conditions  under  which  the  present  experiment  has  been 
made." 


Pot. 

Crossed. 

Self-fert. 

Difference. 

I. 

18J 

19J 

+  0f 

II. 

20  § 

19 

-11 

III. 

21| 

16? 

-H 

IV. 

191 

16 

-H 

"  Next  as  regards  the  numerical  estimate  of  this  excess.  The 
mean  values  of  the  several  groups  are  so  discordant,  as  is  shown 
in  the  table  just  given,  that  a  fairly  precise  numerical  estimate 
seems  impossible.  But  the  consideration  arises,  whether  the 
difference  between  pot  and  pot  may  not  be  of  much  the  same 
order  of  importance  as  that  of  the  other  conditions  upon  which 
the  growth  of  the  plants  has  been  modified.  If  so,  and  only 
on  that  condition,  it  would  follow  that  when  all  the  measure- 
ments, either  of  the  crossed  or  the  self-fertilised  plants,  were 
combined  into  a  single  series,  that  series  would  be  statistically 
regular.  The  experiment  is  tried  in  columns  VII.  and  VIII., 
where  the  regularity  is  abundantly  clear,  and  justifies  us  in 
considering  its  mean  as  perfectly  reliable.  I  have  protracted 
these  measurements,  and  revised  them  in  the  usual  way,  by 
drawing  a  curve  through  them  with  a  free  hand,  but  the  re- 
vision barely  modifies  the  means  derived  from  the  original 
observations.  In  the  present,  and  in  nearly  all  the  other  cases, 
the  difference  between  the  original  and  revised  means  is  under 
2  per  cent,  of  their  value.    It  is  a  very  remarkable  coincidence 


18  INTRODUCTORY   REMARKS.  Chap.  I. 

that  in  the  seven  kinds  of  plants,  whose  measurements  I  have 
examined,  the  ratio  between  the  heights  of  the  crossed  and  of 
the  self-fertilised  ranges  in  five  cases  within  very  narrow  limits. 
In  Zea  mays  it  is  as  100  to  84,  and  in  the  others  it  ranges 
between  100  to  76  and  100  to  86." 

"  The  determination  of  the  variability  (measured  by  what  is 
technically  called  the  '  probable  error ')  is  a  problem  of  more 
delicacy  than  that  of  determining  the  means,  and  I  doubt,  after 
making  many  trials,  whether  it  is  possible  to  derive  useful 
conclusions  from  these  few  observations.  We  ought  to  havo 
measurements  of  at  least  fifty  plants  in  each  case,  in  order  to 
be  in  a  position  to  deduce  fair  results.  One  fact,  however, 
bearing  on  variability,  is  very  evident  in  most  cases,  though  not 
in  Zea  mays,  viz.,  that  the  self-fertilised  plants  include  the 
larger  number  of  exceptionally  small  specimens,  while  tho 
crossed  are  more  generally  full  grown." 

"Those  groups  of  cases  in  which  measurements  have  been 
made  of  a  few  of  the  tallest  plants  that  grew  in  rows,  each  of 
which  contained  a  multitude  of  plants,  show  very  clearly  that 
the  crossed  plants  exceed  the  self-fertilised  in  height,  but  they 
do  not  tell  by  inference  anything  about  their  respective  mean 
values.  If  it  should  happen  that  a  series  is  known  to  follow 
the  law  of  error  or  any  other  law,  and  if  the  number  of  indi- 
viduals in  the  series  is  known,  it  would  be  always  possible  to 
reconstruct  the  whole  series  when  a  fragment  of  it  has  been 
given.  But  I  find  no  such  method  to  be  applicable  in  the 
present  case.  The  doubt  as  to  the  number  of  plants  in  each  row 
is  of  minor  importance ;  the  real  difficulty  lies  in  our  ignorance 
of  the  precise  law  followed  by  the  series.  The  experience  of 
the  plants  in  pots  does  not  help  us  to  determine  that  law, 
because  the  observations  of  such  plants  are  too  few  to  enable 
us  to  lay  down  more  than  the  middle  terms  of  the  series  to 
which  they  belong  with  any  sort  of  accuracy,  whereas  the  cases 
we  are  now  considering  refer  to  one  of  its  extremities.  There 
are  other  special  difficulties  which  need  not  be  gone  into,  as  the 
one  already  mentioned  is  a  complete  bar." 

Mr.  Galton  sent  me  at  the  same  time  graphical 
representations  which  he  had  made  of  the  measure- 
ments, and  they  evidently  form  fairly  regular  curves. 
He  appends  the  words  "  very  good  "  to  those  of  Zea  and 


Chap.  I.  INTKODUCTOBY  EEMAEKS.  19 

Limnanthes.  He  also  calculated  the  average  height 
of  the  crossed  and  self-fertilised  plants  in  the  seven 
tables  by  a  more  correct  method  than  that  followed 
by  me,  namely,  by  including  the  heights,  as  estimated 
in  accordance  with  statistical  rules,  of  a  few  plants 
which  died  before  they  were  measured;  whereas  I 
merely  added  up  the  heights  of  the  survivors,  and 
divided  the  sum  by  their  number.  The  difference  in 
our  results  is  in  one  way  highly  satisfactory,  for 
the  average  heights  of  the  self-fertilised  plants,  as 
deduced  by  Mr.  G-alton,  is  less  than  mine  in  all  the 
cases  excepting  one,  in  which  our  averages  are 
the  same ;  and  this  shows  that  I  have  by  no  means 
exaggerated  the  superiority  of  the  crossed  over  the 
self-fertilised  plants. 

After  the  heights  of  the  crossed  and  self-fertilised 
plants  had  been  taken,  they  were  sometimes  cut  down 
close  to  the  ground,  and  an  equal  number  of  both 
weighed.  This  method  of  comparison  gives  very 
striking  results,  and  I  wish  that  it  had  been  oftener 
followed.  Finally  a  record  was  often  kept  of  any 
marked  difference  in  the  rate  of  germination  of  the 
crossed  and  self -fertilised  seeds, — of  the  relative  periods 
of  flowering  of  the  plants  raised  from  them, — and  of 
their  productiveness,  that  is,  of  the  number  of  seed- 
capsules  which  they  produced  and  of  the  average 
number  of  seeds  which  each  capsule  contained. 

When  I  began  my  experiments  I  did  not  intend  to 
raise  crossed  and  self-fertilised  plants  for  more  than  a 
single  generation ;  but  as  soon  as  the  plants  of  the 
first  generation  were  in  flower  I  thought  that  I  would 
~aise  one  more  generation,  and  acted  in  the  following 
manner.  Several  flowers  on  one  or  more  of  the  self- 
fertilised  plants  were  again  self-fertilised  ;  and  several 


20  INTRODUCTORY   REMARKS.  Chap.  I. 

flowers  on  one  or  more  of  the  crossed  plants  were  ferti- 
lised with  pollen  from  another  crossed  plant  of  the 
same  lot.  Having  thus  once  begun,  the  same  method 
was  followed  for  as  many  as  ten  successive  generations 
with  some  of  the  species.  The  seeds  and  seedlings  were 
always  treated  in  exactly  the  same  manner  as  already 
described.  The  self-fertilised  plants,  whether  originally 
descended  from  one  or  two  mother-plants,  were  thus  in 
each  generation  as  closely  interbred  as  was  possible ; 
and  I  could  not  have  improved  on  my  plan.  But 
instead  of  crossing  one  of  the  crossed  plants  with 
another  crossed  plant,  I  ought  to  have  crossed  the  self- 
fertilised  plants  of  each  generation  with  pollen  taken 
from  a  non-related  plant — that  is,  one  belonging  to  a 
distinct  family  or  stock  of  the  same  species  and  variety. 
This  was  done  in  several  cases  as  an  additional  experi- 
ment, and  gave  very  striking  results.  But  the  plan 
usually  followed  was  to  put  into  competition  and 
compare  intercrossed  plants,  which  were  almost  always 
the  offspring  of  more  or  less  closely  related  plants,  with 
the  self-fertilised  plants  of  each  succeeding  genera- 
tion ; — all  having  been  grown  under  closely  similar 
conditions.  I  have,  however,  learnt  more  by  this  method 
of  proceeding,  which  was  begun  by  an  oversight  and 
then  necessarily  followed,  than  if  I  had  always  crossed 
the  self-fertilised  plants  of  each  succeeding  generation 
with  pollen  from  a  fresh  stock. 

I  have  said  that  the  crossed  plants  of  the  successive 
generations  were  almost  always  inter-related.  When 
the  flowers  on  an  hermaphrodite  plant  are  crossed 
with  pollen  taken  from  a  distinct  plant,  the  seedlings 
thus  raised  may  be  considered  as  hermaphrodite  brothers 
or  sisters  ;  those  raised  from  the  same  capsule  being  as 
close  as  twins  or  animals  of  the  same  litter.  But  in 
one  sense  the  flowers  on  the  same  plant  are  distinct 


Chap.  I.  INTEODUCTOEY   EEMAEKS.  21 

individuals,  and  as  several  flowers  on  the  mother-plant 
were  crossed  by  pollen  taken  from  several  flowers  on 
the  father-plant,  such  seedlings  would  be  in  one  sense 
half-brothers  or  sisters,  but  more  closely  related  than 
are  the  half-brothers  and  sisters  of  ordinary  animals. 
The  flowers  on  the  mother-plant  were,  however,  com- 
monly crossed  by  pollen  taken  from  two  or  more  dis- 
tinct plants ;  and  in  these  cases  the  seedlings  might 
be  called  with  more  truth  half-brothers  or  sisters. 
When  two  or  three  mother-plants  were  crossed,  as  often 
happened,  by  pollen  taken  from  two  or  three  father- 
plants  (the  seeds  being  all  intermingled),  some  of  the 
seedlings  of  the  first  generation  would  be  in  no  way 
related,  whilst  many  others  would  be  whole  or  half- 
brothers  and  sisters.  In  the  second  generation  a  large 
number  of  the  seedlings  would  be  what  may  be  called 
whole  or  half  first-cousins,  mingled  with  whole  and 
half-brothers  and  sisters,  and  with  some  plants  not  at 
all  related.  So  it  would  be  in  the  succeeding  genera- 
tions, but  there  would  also  be  many  cousins  of  the 
second  and  more  remote  degrees.  The  relationship  will 
thus  have  become  more  and  more  inextricably  complex 
in  the  later  generations  ;  with  most  of  the  plants  in 
some  degree  and  many  of  them  closely  related. 

I  have  only  one  other  point  to  notice,  but  this  is  one 
of  the  highest  importance;  namely,  that  the  crossed 
and  self-fertilised  plants  were  subjected  in  the  same 
generation  to  as  nearly  similar  and  uniform  conditions  as 
was  possible.  In  the  successive  generations  they  were 
exposed  to  slightly  different  conditions  as  the  seasons 
varied,  and  they  were  raised  at  different  periods.  But 
in  other  respects  all  were  treated  alike,  being  grown 
in  pots  in  the  same  artificially  prepared  soil,  being 
watered  at  the  same  time,  and  kept  close  together 
in   the    same    greenhouse   or   hothouse.     They   were 


22  INTEODUCTOEY  EEMAEES.  Chap.  I 

therefore  not  exposed  during  successive  years  to  such 
great  vicissitudes  of  climate  as  are  plants  growing  out 
of  doors. 

On  some  apparent  and  real  Causes  of  Error  in  my  Ex- 
periments.— It  has  been  objected  to  such  experiments 
as  mine,  that  covering  plants  with  a  net,  although  only 
for  a  short  time  whilst  in  flower,  may  affect  their  health 
and  fertility.  I  have  seen  no  such  effect  except  in  one 
instance  with  a  Myosotis,  and  the  covering  may  not 
then  have  been  the  real  cause  of  injury.  But  even  if 
the  net  were  slightly  injurious,  and  certainly  it  was  not 
so  in  any  high  degree,  as  I  could  judge  by  the  appear- 
ance of  the  plants  and  by  comparing  their  fertility  with 
that  of  neighbouring  uncovered  plants,  it  would  not 
have  vitiated  my  experiments ;  for  in  all  the  more  im- 
portant cases  the  flowers  were  crossed  as  well  as  self- 
fertilised  under  a  net,  so  that  they  were  treated  in  this 
respect  exactly  alike. 

As  it  is  impossible  to  exclude  such  minute  pollen- 
carrying  insects  as  Thrips,  flowers  which  it  was  intended 
to  fertilise  with  their  own  pollen  may  sometimes  have 
been  afterwards  crossed  with  pollen  brought  by  these 
insects  from  another  flower  on  the  same  plant ;  but  as 
we  shall  hereafter  see,  a  cross  of  this  kind  does  not 
produce  any  effect,  or  at  most  only  a  slight  one.  WheD 
two  or  more  plants  were  placed  near  one  anothei 
under  the  same  net,  as  was  often  done,  there  is  some 
real  though  not  great  danger  of  the  flowers  which 
were  believed  to  be  self-fertilised  being  afterward? 
crossed  with  pollen  brought  by  Thrips  from  a  distinct 
plant.  I  have  said  that  the  danger  is  not  great 
because  I  have  often  found  that  plants  which  are 
self-sterile,  unless  aided  by  insects,  remained  sterile 
when  several  plants  of  the  same  species  were  placed 


Chap.  I.  INTRODUCTORY  REMARKS.  23 

under  the  same  net.  If,  however,  the  flowers  which 
had  been  presumably  self -fertilised  by  me  were  in  any 
case  afterwards  crossed  by  Thrips  with  pollen  brought 
from  a  distinct  plant,  crossed  seedlings  would  have 
been  included  amongst  the  self-fertilised  ;  but  it  should 
be  especially  observed  that  this  occurrence  would  tend 
to  diminish  and  not  to  increase  any  superiority  in 
average  height,  fertility,  &c,  of  the  crossed  over  the 
self-fertilised  plants. 

As  the  flowers  which  were  crossed  were  never  cas- 
trated, it  is  probable  or  even  almost  certain  that  I 
sometimes  failed  to  cross-fertilise  them  effectually,  and 
that  they  were  afterwards  spontaneously  self-fertilised. 
This  would  have  been  most  likely  to  occur  with  dicho- 
gamous  species,  for  without  much  care  it  is  not  easy  to 
perceive  whether  their  stigmas  are  ready  to  be  fer- 
tilised when  the  anthers  open.  But  in  all  cases, 
as  the  flowers  were  protected  from  wind,  rain,  and  the 
access  of  insects,  any  pollen  placed  by  me  on  the 
stigmatic  surface  whilst  it  was  immature,  would  gener- 
ally have  remained  there  until  the  stigma  was  mature  ; 
and  the  flowers  would  then  have  been  crossed  as  was 
intended.  Nevertheless,  it  is  highly  probable  that 
self-fertilised  seedlings  have  sometimes  by  this  means 
got  included  amongst  the  crossed  seedlings.  The  effect 
would  be,  as  in  the  former  case,  not  to  exaggerate 
but  to  diminish  any  average  superiority  of  the  crossed 
over  the  self-fertilised  plants. 

Errors  arising  from  the  two  causes  just  named,  and 
from  others, — such  as  some  of  the  seeds  not  having 
been  thoroughly  ripened,  though  care  was  taken  to 
avoid  this  error — the  sickness  or  unperceived  injury  of 
any  of  the  plants, — will  have  been  to  a  large  extent 
eliminated,  in  those  cases  in  which  many  crossed  and 
self-fertilised   plants  were   measured  and  an   average 


24  INTRODUCTOEY  EEMAEKS.  Chap.  L 

struck.  Some  of  these  causes  of  error  will  also  have 
been  eliminated  by  the  seeds  having  been  allowed  to 
germinate  on  bare  damp  sand,  and  being  planted  in 
pairs ;  for  it  is  not  likely  that  ill-matured  and  well- 
matured,  or  diseased  and  healthy  seeds,  would  germi- 
nate at  exactly  the  same  time.  The  same  result  will 
have  been  gained  in  the  several  cases  in  which  only  a 
few  of  the  tallest,  finest,  and  healthiest  plants  on  each 
side  of  the  pots  were  measured. 

Kolreuter  and  Gartner*  have  proved  that  with  some 
plants  several,  even  as  many  as  from  fifty  to  sixty, 
pollen-grains  are  necessary  for  the  fertilisation  of  all 
the  ovules  in  the  ovarium.  Naudin  also  found  in 
the  case  of  Mirabilis  that  if  only  one  or  two  of  its 
very  large  pollen-grains  were  placed  on  the  stigma, 
the  plants  raised  from  such  seeds  were  dwarfed. 
I  was  therefore  careful  to  give  an  amply  sufficient 
supply  of  pollen,  and  generally  covered  the  stigma 
with  it ;  but  I  did  not  take  any  special  pains  to  place 
exactly  the  same  amount  on  the  stigmas  of  the  self- 
fertilised  and  crossed  flowers.  After  having  acted  in 
this  manner  during  two  seasons,  I  remembered  that 
Gartner  thought,  though  without  any  direct  evidence, 
that  an  excess  of  pollen  was  perhaps  injurious ;  and  it 
has  been  proved  by  Spallanzani,  Quatrefages,  and 
Newport,!  that  with  various  animals  an  excess  of  the 
seminal  fluid  entirely  prevents  fertilisation.  It  was 
therefore  necessary  to  ascertain  whether  the  fertility  of 
the  flowers  was  affected  by  applying  a  rather  small  and 
an  extremely  large  quantity  of  pollen  to  the  stigma. 
Accordingly  a  very  small  mass  of  pollen-grains  was 


*  '  Keimtuiss     der     Befruch-       torn.  i.  p.  27. 
tung,'    1844,    p.    345.      Naudin,  f  'Transactions    Philosophical 

•  Nouvelles  Archives  du  Museum,'       Soc.'  1853,  pp.  253-258. 


Chap.  I.  INTRODUCTORY  REMARKS.  25 

placed  on  one  side  of  the  large  stigma  in  sixty-four 
flowers  of  Ipomoea  purpurea,  and  a  great  mass  of  pollen 
over  the  whole  surface  of  the  stigma  in  sixty -four  other 
flowers.  In  order  to  vary  the  experiment,  half  the 
flowers  of  both  lots  were  on  plants  produced  from  self- 
fertilised  seeds,  and  the  other  half  on  plants  from 
crossed  seeds.  The  sixty-four  flowers  with  an  excess 
of  pollen  yielded  sixty-one  capsules ;  and  excluding 
four  capsules,  each  of  which  contained  only  a  single 
poor  seed,  the  remainder  contained  on  an  average  5  ■  07 
seeds  per  capsule.  The  sixty -four  flowers  with  only  a 
little  pollen  placed  on  one  side  of  the  stigma  yielded 
sixty-three  capsules,  and  excluding  one  from  the  same 
cause  as  before,  the  remainder  contained  on  an  average 
5  •  129  seeds.  So  that  the  flowers  fertilised  with  little 
pollen  yielded  rather  more  capsules  and  seeds  than  did 
those  fertilised  with  an  excess ;  but  the  difference  is 
too  slight  to  be  of  any  significance.  On  the  other 
hand,  the  seeds  produced  by  the  flowers  with  an  excess 
of  pollen  were  a  little  heavier  of  the  two ;  for  170  of 
them  weighed  79  *  67  grains,  whilst  170  seeds  from  the 
flowers  with  very  little  pollen  weighed  79  ■  20  grains. 
Both  lots  of  seeds  having  been  placed  on  damp  sand 
presented  no  difference  in  their  rate  of  germination. 
We  may  therefore  conclude  that  my  experiments  were 
not  affected  by  any  slight  difference  in  the  amount  of 
pollen  used ;  a  sufficiency  having  been  employed  in 
all  cases. 

The  order  in  which  our  subject  will  be  treated  in 
the  present  volume  is  as  follows.  A  long  series  of  ex- 
periments will  first  be  given  in  Chapters  II.  to  YI. 
Tables  will  afterwards  be  appended,  showing  in  a  con- 
densed form  the  relative  heights,  weights,  and  fertility 
of  the  offspring  of  the  various  crossed  and  self-fertilised 


26  INTRODUCTORY   REMARKS.  Chap.  L 

species.  Another  table  exhibits  the  striking  results 
from  fertilising  plants,  which  during  several  generations 
had  either  been  self-fertilised  or  had  been  crossed 
with  plants  kept  all  the  time  under  closely  similar 
conditions,  with  pollen  taken  from  plants  of  a  distinct 
stock  and  which  had  been  exposed  to  different  con- 
ditions. In  the  concluding  chapters  various  related 
points  and  questions  of  general  interest  will  be 
discussed. 

Anyone  not  specially  interested  in  the  subject  need 
not  attempt  to  read  all  the  details ;  though  they 
possess,  I  think,  some  value,  and  cannot  be  all  sum- 
marised. But  I  would  suggest  to  the  reader  to  take 
as  an  example  the  experiments  on  Ipoinoea  in  Chapter 
II. ;  to  which  may  be  added  those  on  Digitalis,  Origa- 
num, Viola,  or  the  common  cabbage,  as  in  all  these 
cases  the  crossed  plants  are  superior  to  the  self- 
fertilised  in  a  marked  degree,  but  not  in  quite  the 
same  manner.  As  instances  of  self-fertilised  plants 
being  equal  or  superior  to  the  crossed,  the  experiments 
on  Bartonia,  Canna,  and  the  common  pea  ought  to  be 
read;  but  in  the  last  case,  and  probably  in  that  of 
Canna,  the  want  of  any  superiority  in  the  crossed 
plants  can  be  explained. 

Species  were  selected  for  experiment  belonging  to 
widely  distinct  families,  inhabiting  various  countries. 
In  some  few  cases  several  genera  belonging  to  the 
same  family  were  tried,  and  these  are  grouped  toge- 
ther ;  but  the  families  themselves  have  been  arranged 
not  in  any  natural  order,  but  in  that  which  was  the 
most  convenient  for  my  purpose.  The  experiments 
have  been  fully  given,  as  the  results  appear  to  me  of 
sufficient  value  to  justify  the  details.  Plants  bearing 
hermaphrodite  flowers  can  be  interbred  more  closely 
than  is  possible  with  bisexual  animals,  and  are  there* 


Chap.  I.  INTRODUCTORY   REMARKS.  27 

fore  well-fitted  to  throw  light  on  the  nature  and  extent 
of  the  good  effects  of  crossing,  and  on  the  evil  effects 
of  close  interbreeding  or  self-fertilisation.  The  most 
important  conclusion  at  which  I  have  arrived  is  that 
the  mere  act  of  crossing  by  itself  does  no  good.  The 
good  depends  on  the  individuals  which  are  crossed 
differing  slightly  in  constitution,  owing  to  their  pro- 
genitors having  been  subjected  during  several  genera- 
tions to  slightly  different  conditions,  or  to  what  we 
call  in  our  ignorance  spontaneous  variation.  This 
conclusion,  as  we  shall  hereafter  see,  is  closely  con- 
nected with  various  important  physiological  problems, 
such  as  the  benefit  derived  from  slight  changes  in  the 
conditions  of  life,  and  this  stands  in  the  closest  con- 
nection with  life  itself.  It  throws  light  on  the  origin  of 
the  two  sexes  and  on  their  separation  or  union  in  the 
same  individual,  and  lastly  on  the  whole  subject  of 
hybridism,  which  is  one  of  the  greatest  obstacles  to  the 
general  acceptance  and  progress  of  the  great  principle 
of  evolution. 

In  order  to  avoid  misapprehension,  I  beg  leave  to 
repeat  that  throughout  this  volume  a  crossed  plant, 
seedling,  or  seed,  means  one  of  crossed  parentage,  that 
is,  one  derived  from  a  flower  fertilised  with  pollen 
from  a  distinct  plant  of  the  same  species.  And  that 
a  self-fertilised  plant,  seedling,  or  seed,  means  one 
of  self-fertilised  parentage,  that  is,  one  derived  from 
a  flower  fertilised  with  pollen  from  the  same  flower, 
or  sometimes,  when  thus  stated,  from  another  flower 
on  the  same  plant. 


28  IFOMCEA  PURPUREA.  Chap.  li. 


CHAPTER  II. 

CONVOLVULACE^S. 

Ipomoea  purpurea,  comparison  of  the  height  and  fertility  of  the 
crossed  and  self-fertilised  plants  during  ten  successive  generations 
— Greater  constitutional  vigour  of  the  crossed  plants — The  effects 
on  the  offspring  of  crossing  different  flowers  on  the  same  plant, 
instead  of  crossing  distinct  individuals — The  effects  of  a  cross  with 
a  fresh  stock — The  descendants  of  the  self-fertilised  plant  named 
Hero — Summary  on  the  growth,  vigour,  and  fertility  of  the  suc- 
cessive crossed  and  self-fertilised  generations — Small  amount  of 
pollen  in  the  anthers  of  the  self-fertilised  plants  of  the  later  genera- 
tions, and  the  sterility  of  their  first-produced  flowers — Uniform 
colour  of  the  flowers  produced  hy  the  self-fertilised  plants — The 
advantage  from  a  cross  between  two  distinct  plants  depends  on  their 
differing  in  constitution. 

A  plant  of  Ipomoea  purpurea,  or  as  it  is  often  called  in 
England  the  convolvulus  major,  a  native  of  South 
America,  grew  in  my  greenhouse.  Ten  flowers  on  this 
plant  were  fertilised  with  pollen  from  the  same  flower ; 
and  ten  other  flowers  on  the  same  plant  were  crossed 
with  pollen  from  a  distinct  plant.  The  fertilisation  of 
the  flowers  with  their  own  pollen  was  superfluous,  as 
this  convolvulus  is  highly  self-fertile ;  but  I  acted  in 
this  manner  to  make  the  experiments  correspond  in  all 
respects.  Whilst  the  flowers  are  young  the  stigma 
projects  beyond  the  anthers ;  and  it  might  have  been 
thought  that  it  could  not  be  fertilised  without  the  aid 
of  humble-bees,  which  often  visit  the  flowers ;  but  as 
the  flower  grows  older  the  stamens  increase  in  length, 
and  their  anthers  brush  against  the  stigma,  which  thus 


Chap.  II.     CEOSSED   AND   SELF-FERTILISED   PLANTS. 


29 


receives  some  pollen.  The  number  of  seeds  produced 
by  the  crossed  and  self-fertilised  flowers  differed  very 
little. 

Crossed  and  self-fertilised  seeds  obtained  in  the  above 
manner  were  allowed  to  germinate  on  damp  sand,  and  as  often 
as  pairs  germinated  at  the  same  time  they  were  planted  in  the 
manner  described  in  the  Introduction,  on  the  opposite  sides  of 
two  pots.  Five  pairs  were  thns  planted ;  and  all  the  remaining 
seeds,  whether  or  not  in  a  state  of  germination,  were  planted  on 
the  opposite  sides  of  a  third  pot,  so  that  the  young  plants  on 
both  sides  were  here  greatly  crowded  and  exposed  to  very 
severe  competition.  Rods  of  iron  or  wood  of  equal  diameter 
were  given  to  all  the  plants  to  twine  up;  and  as  soon  as  one  of 
each  pair  reached  the  summit  both  were  measured.  A  single 
rod  was  placed  on  each  side  of  the  crowded  pot,  No.  ILL,  and 
only  the  tallest  plant  on  each  side  was  measured. 

Table  I.  (First  Generation.) 


No.  of  Pot. 

Seedlings  from              Seedlings  from 
Crossed  Plants.       |  Self-fertilised  Plants. 

I. 

Inches. 
87 1 
87^ 
89 

Inches. 
69 
66 
73 

II. 

88 
87 

68 1 
60| 

III. 

Plants  crowded ;  the 
tallest    one    mea- 
sured on  each  side. 

77 

57 

Total  in  inches. 

516 

S94 

The  average  height  of  the  six  crossed  plants  is  here  86  inches, 
whilst  that  of  the  six  self-fertilised  plants  is  only  65  ■  66  inches, 
so  that  the  crossed  plants  are  to  the  self-fertilised  in  height  as 
100  to  76.  It  should  be  observed  that  this  difference  is  not  due 
to  a  few  of  the  crossed  plants  being  extremely  tall,  or  to  a  few  of 
the  self-fertilised  being  extremely  short,  but  to  all  the  crossed 
plants  attaining  a  greater  height  than  their  antagonists.  The 
three  pairs  in  Pot  I.  were  measured  at  two  earlier  periods,  and 
the  difference  was  sometimes  greater  and  sometimes  less  than  that 


30  IPOMCEA  PURPUREA.  Chap.  IT. 

at  the  final  measuring.  But  it  is  an  interesting  fact,  of  which.  I 
have  seen  several  other  instances,  that  one  of  the  self-fertilised 
plants,  when  nearly  a  foot  in  height,  was  half  an  inch  taller  than 
the  crossed  plant;  and  again,  when  two  feet  high,  it  was  If  of 
an  inch  taller,  but  during  the  ten  subsequent  days  the  crossed 
plant  began  to  gain  on  its  antagonist,  and  ever  afterward  asserted 
its  supremacy,  until  it  exceeded  its  self-fertilised  opponent  by 
16  inches. 

The  five  crossed  plants  in  Pots  I.  and  II.  were  covered  with  a 
net,  and  produced  121  capsules ;  the  five  self-fertilised  plants 
produced  eighty-four  capsules,  so  that  the  numbers  of  capsules 
were  as  100  to  69.  Of  the  121  capsules  on  the  crossed  plants 
sixty-five  were  the  product  of  flowers  crossed  with  pollen  from  a 
distinct  plant,  and  these  contained  on  an  average  5  ■  23  seeds  per 
capsule;  the  remaining  fifty-six  capsules  were  spontaneously 
self-fertilised.  Of  the  eighty-four  capsules  on  the  self-fertilised 
plants,  all  the  product  of  renewed  self-fertilisation,  fifty-five 
(which  were  alone  examined)  contained  on  an  average  4*85 
seeds  per  capsule.  Therefore  the  cross-fertilised  capsules,  com- 
pared with  the  self-fertilised  capsules,  yielded  seeds  in  the 
proportion  of  100  to  93.  The  crossed  seeds  were  relatively 
heavier  than  the  self-fertilised  seeds.  '  Combining  the  above 
data  (i.e.,  number  of  capsules  and  average  number  of  contained 
seeds),  the  crossed  plants,  compared  with  the  self-fertilised, 
yielded  seeds  in  the  ratio  of  100  to  64. 

These  crossed  plants  produced,  as  already  stated,  fifty-six 
spontaneously  self-fertilised  capsules,  and  the  self-fertilised 
plants  produced  twenty-nine  such  capsules.  The  former  con- 
tained on  an  average,  in  comparison  with  the  latter,  seeds 
in  the  proportion  of  100  to  99. 

In  Pot  III.,  on  the  opposite  sides  of  which  a  large  number  of 
crossed  and  self-fertilised  seeds  had  been  sown  and  the  seed- 
lings allowed  to  struggle  together,  the  crossed  plants  had  at 
first  no  great  advantage.  At  one  time  the  tallest  crossed  was 
25i  inches  high,  and  the  tallest  self-fertilised  plants  21|.  But 
the  difference  afterwards  became  much  greater.  The  plants  on 
both  sides,  from  being  so  crowded,  were  poor  specimens.  The 
flowers  were  allowed  to  fertilise  themselves  spontaneously  under 
a  net;  the  crossed  plants  produced  thirty-seven  capsules,  the 
self-fertilised  plants  only  eighteen,  or  as  100  to  47.  The  former 
contained  on  an  average  3  •  62  seeds  per  capsule ;  and  the  latter 
3  "38  seeds,  or  as  100  to  93.     Combining  these  data  (i.e.,  number 


Chap.  II.     CROSSED   AND    SELF-FERTILISED   PLANTS.        3] 


of  capsules  and  average  number  of  seeds),  the  crowded  crossed 
plants  produced  seeds  compared  with  the  self-fertilised  as  100 
to  45.  These  latter  seeds,  however,  were  decidedly  heavier,  a 
hundred  weighing  41  ■  64  grains,  than  those  from  the  capsules 
on  the  crossed  plants,  of  which  a  hundred  weighed  36  ■  79  grains ; 
and  this  probably  was  due  to  the  fewer  capsules  borne  by  tho 
self-fertilised  plants  having  been  better  nourished.  We  thus  see 
that  the  crossed  plants  in  this  the  first  generation,  when  grown 
under  favourable  conditions,  and  when  grown  under  unfavour- 
able conditions  from  being  much  crowded,  greatly  exceeded  in 
height,  and  in  the  number  of  capsules  produced,  and  slightly 
in  the  number  of  seeds  per  capsule,  the  self-fertilised  plants. 

Grossed  and  self-fertilised  Plants  of  the  Second  Generation. — 
Flowers  on  the  crossed  plants  of  the  last  generation  (Table  I.) 
were  crossed  by  pollen  from  distinct  plants  of  the  same  genera- 
tion ;  and  flowers  on  the  self-fertilised  plants  were  fertilised  by 
pollen  from  the  same  flower.  The  seeds  thus  produced  were 
treated  in  every  respect  as  before,  and  we  have  in  Table  II. 
the  result. 

Table  II.  {Second  Generation.') 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
87 
83 
83 

Inches. 
67| 
68! 
80! 

II. 

85 1 

89 

77| 

61| 

79 
41 

Total  inches. 

505 

398 

Here  again  every  single  crossed  plant  is  taller  than  its  anta- 
gonist. The  self-fertilised  plant  in  Pot  I.,  which  ultimately 
reached  the  unusual  height  of  80|  inches,  was  for  a  long  time 
taller  than  the  opposed  crossed  plant,  though  at  last  beaten  by 
it.  The  average  height  of  the  six  crossed  plants  is  84"  16  inches, 
whilst  that  of  the  six  self-fertilised  plants  is  66*33  inches,  or 
as  100  to  79. 

Crossed  and  self -fertilised  Plants  of  the  Third  Generation. — Seeds 
from  the  crossed  plants  of  the  last  generation  (Table  II.)  again 


32 


IPOMCEA   PURPUREA. 


Chap.  11. 


crossed,  and  from  the  self-fertilised  plants  again  self-fertilised, 
were  treated  in  all  respects  exactly  as  before,  with  the  following 
result : — 

Table  III.  {Third  Generation.) 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
74 
72 
73 1 

Inches. 
56 1 
51 1 

54 

II. 

82 
81 
82 

59 
30 
66 

Total  inches. 

464-5 

317-0 

Again  all  the  crossed  plants  are  higher  than  their  antagonists : 
their  average  height  is  77  "41  inches,  whereas  that  of  the  self- 
fertilised  is  52  •  83  inches,  or  as  100  to  68. 

I  attended  closely  to  the  fertility  of  the  plants  of  this  third 
generation.  Thirty  flowers  on  the  crossed  plants  were  crossed 
with  pollen  from  other  crossed  plants  of  the  same  generation, 
and  the  twenty-sis  capsules  thus  produced  contained,  on  an 
average,  4 -73  seeds;  whilst  thirty  flowers' on  the  self-fertilised 
plants,  fertilised  with  the  pollen  from  the  same  flower,  produced 
twenty-three  capsules,  each  containing  4-43  seeds.  Thus  the 
average  number  of  seeds  in  the  crossed  capsules  was  to  that  in 
the  self-fertilised  capsules  as  100  to  94.  A  hundred  of  the 
crossed  seeds  weighed  43  ■  27  grains,  whilst  a  hundred  of  the  self- 
fertilised  seeds  weighed  only  37  ■  63  grains.  Many  of  these  lighter 
self-fertilised  seeds  placed  on  damp  sand  germinated  before  the 
crossed ;  thus  thirty-sis  of  the  former  germinated  whilst  only 
thirteen  of  the  latter  or  crossed  seeds  germinated.  In  Pot  I. 
the  three  crossed  plants  produced  spontaneously  under  the  net 
(besides  the  twenty-six  artificially  cross-fertilised  capsules) 
seventy-seven  self-fertilised  capsules  containing  on  an  average 
4*41  seeds;  whilst  the  three  self-fertilised  plants  produced 
spontaneously  (besides  the  twenty-three  artificially  self-fertilised 
capsules)  only  twenty-nine  self-fertilised  capsules,  containing  on 
an  average  4  ■  14  seeds.  Therefore  the  average  number  of  seeds 
in  the  two  lots  of  spontaneously  self-fertilised  capsules  was  as 


Chap.  II.     CROSSED   AND   SELF-FERTILISED   PLANTS. 


S3 


100  to  94.  Taking  into  consideration  the  number  of  capsules 
together  with  the  average  number  of  seeds,  the  crossed  plants 
(spontaneously  self-fertilised)  produced  seeds  in  comparison  with 
the  self-fertilised  plants  (spontaneously  self-fertilised)  in  the 
proportion  of  100  to  35.  By  whatever  method  the  fertility  of 
these  plants  is  compared,  the  crossed  are  more  fertile  than  the 
self-fertilised  plants. 

I  tried  in  several  ways  the  comparative  vigour  and  powers  of 
growth  of  the  crossed  and  self-fertilised  plants  of  this  third 
generation.  Thus,  four  self-fertilised  seeds  which  had  just 
germinated  were  planted  on  one  side  of  a  pot,  and  after  an  in- 
terval of  fOrty-eight  hours,  four  crossed  seeds  in  the  same  state 
of  germination  were  planted  on  the  opposite  side ;  and  the  pot 
was  kept  in  the  hothouse.  I  thought  that  the  advantage  thus 
given  to  the  self-fertilised  seedlings  would  have  been  so  great 
that  they  would  never  have  been  beaten  by  the  crossed  ones. 
They  were  not  beaten  until  all  had  grown  to  a  height  of  18 
inches;  and  the  degree  to  which  they  were  finally  beaten  is 
shown  in  the  following  table  (No.  IV.).  We  here  see  that  the 
average  height  of  the  four  crossed  plants  is  76  ■  62,  and  of  the 
four  self-fertilised  plants  65  ■  87  inches,  or  as  100  to  86 ;  there- 
fore less  than  when  both  sides  started  fair. 

TABLE  TV.  {Third  Generation,  the  self-fertilised  Plants  having 
had  a  start  of  forty-eight  hours.) 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants 

III. 

Inches. 
78| 
77$ 

73 
77 1 

Inches. 
73| 
53 
61 1 
75| 

Total  inches. 

306-5 

263-5 

Crossed  and  self-fertilised  seeds  of  the  third  generation  were 
also  sown  out  of  doors  late  in  the  summer,  and  therefore  under 
unfavourable  conditions,  and  a  single  stick  was  given  to  each 
lot  of  plants  to  twine  up.  The  two  lots  were  sufficiently 
separate  so  as  not  to  interfere  with  each  other's  growth,  and  the 
ground  was  clear  of  weeds.  As  soon  as  they  were  killed  by  the 
first  frost  (and  there  was  no  difference  in  their  hardiness),  the 
two  tallest  crossed  plants  were  found  to  be  24- 5  and  22*  5  inches, 


34 


IPOMCEA   PURPUKEA. 


Chap.  II. 


whilst  the  two  tallest  self-fertilised  plants  were  only  15  and 
12  •  5  inches  in  height,  or  as  100  to  59. 

I  likewise  sowed  at  the  same  time  two  lots  of  the  same  seeds 
in  a  part  of  the  garden  which  was  shady  and  covered  with 
weeds.  The  crossed  seedlings  from  the  first  looked  the  most 
healthy,  but  they  twined  np  a  stick  only  to  a  height  of  7i  inches ; 
whilst  the  self-fertilised  were  not  able  to  twine  at  all ;  and  the 
tallest  of  them  was  only  3i  inches  in  height. 

Lastly,  two  lots  of  the  same  seeds  were  sown  in  the  midst  of 
a  bed  of  candy-tuft  (Iberis)  growing  vigorously.  The  seedlings 
came  up,  but  all  the  self-fertilised  ones  soon  died  excepting  one, 
which  never  twined ''and  grew  to  a  height  of  only  4  inches. 
Many  of  the  crossed  seedlings,  on  the  other  hand,  survived; 
and  some  twined  up  the  stems  of  the  Iberis  to  the  height  of 
11  inches.  These  cases  prove  that  the  crossed  seedlings 
have  an  immense  advantage  over  the  self-fertilised,  both  when 
growing  isolated  under  very  unfavourable  conditions,  and  when 
put  into  competition  with  each  other  or  with  other  plants,  as 
would  happen  in  a  state  of  nature. 

Crossed  and  self-fertilised  Plants  of  the  Fourth  Generation. — Seed- 
lings raised  as  before  from  the  crossed  and  self-fertilised  plants 
of  the  third  generation  in  Table  III.,  gave  results  as  follows : — 

Table  V.  (Fourth  Generation.") 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 

8-i 
47 

Inches. 
80 
44 1 

II.                                 83 

59 

73  i 
51J 

III. 

82 
65 | 

68 

56| 

63 

52 

Total  inches. 

488-5 

421-0 

Here  the  average  height  of  the  seven  crossed  plants  is  69 '  78 
inches,  and  that  of  the  seven  self-fertilised  plants  60 '  14 ;  or  as 
100  to  86.  This  smaller  difference  relatively  to  that  in  the 
former  generations,  may  be  attributed  to  the  plants  having  been 
raised  during  the  depth  of  winter,  and  consequently  to  their  not 


Chap.  II.     GROSSED   AND   SELF-FEBTILISED   PLANTS. 


35 


having  grown  vigorously,  as  was  shown  by  their  general  ap- 
pearance and  from  several  of  them  never  reaching  the  summits 
of  the  rods.  In  Pot  II.,  one  of  the  self-fertilised  plants  was  for 
a  long  time  taller  by  two  inches  than  its  opponent,  but  was 
ultimately  beaten  by  it,  so  that  all  the  crossed  plants  exceeded 
their  opponents  in  height.  Of  twenty-eight  capsules  produced 
by  the  crossed  plants  fertilised  by  pollen  from  a  distinct  plant, 
each  contained  on  an  average  4 "75  seeds;  of  twenty-seven  self- 
fertilised  capsules  on  the  self-fertilised  plants,  each  contained 
on  an  average  4*47  seeds;  so  that  the  proportion  of  seeds  in  the 
crossed  and  self-fertilised  capsules  was  as  100  to  94. 

Some  of  the  same  seeds,  from  which  the  plants  in  the  last 
Table  V.  had  been  raised,  were  planted,  after  they  had  germi- 
nated on  damp  sand,  in  a  square  tub,  in  which  a  large  Brug- 
mansia  had  long  been  growing.  The  soil  was  extremely  poor 
and  full  of  roots ;  six  crossed  seeds  were  planted  in  one  corner, 
and  six  self-fertilised  seeds  in  the  opposite  corner.  All  the 
seedlings  from  the  latter  soon  died  excepting  one,  and  this  grew 
to  the  height  of  only  li  inches.  Of  the  crossed  plants  three 
survived,  and  they  grew  to  the  height  of  2|  inches,  but  were  not 
able  to  twine  round  a  stick ;  nevertheless,  to  my  surprise,  they 
produced  some  small  miserable  flowers.  The  crossed  plants 
thus  had  a  decided  advantage  over  the  self-fertilised  plants 
under  this  extremity  of  bad  conditions. 

C rossed  and  self  fertilised  Plants  of  the  Fifth  Generation. — These 
were  raised  in  the  same  manner  as  before,  and  when  measured 
gave  the  following  results : — 

Table  YI.  (Fifth  Generation.) 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
96 
86 
69 

Inches. 
73 

78 
29 

II. 

84 
84 
76 1 

51 

84 
59 

Total  inches. 

495-25 

374 -00 

The  average  height  of  the  six  crossed  plants  is  82  ■  54  inchesf 


36 


IPOMCEA   PUKPUREA. 


Chap.IL 


and  that  of  the  six  self-fertilised  plants  62  ■  33  inches,  or  as  100 
to  75.  Every  crossed  plant  exceeded  its  antagonist  in  height. 
In  Pot  I.  the  middle  plant  on  the  crossed  side  was  slightly- 
injured  whilst  young  by  a  blow,  and  was  for  a  time  beaten  by 
its  opponent,  but  ultimately  recovered  the  usual  superiority. 
The  crossed  plants  produced  spontaneously  a  vast  number  more 
capsules  than  did  the  self-fertilised  plants ;  and  the  capsules  of 
the  former  contained  on  an  average  3 "  37  seeds,  whilst  those  of 
the  latter  contained  only  3  ■  0  per  capsule,  or  as  100  to  89.  But 
looking  only  to  the  artificially  fertilised  capsules,  those  on  the 
crossed  plants  again  crossed  contained  on  an  average  4  "46 
seeds,  whilst  those  on  the  self-fertilised  plants  again  self- 
fertilised  contained  4*77  seeds;  so  that  the  self-fertilised  cap- 
sules were  the  more  fertile  of  the  two,  and  of  this  unusual  fact 
I  can  offer  no  explanation. 

Crossed  and  self  fertilised  Plants  of  the  Sixth  Generation. — 
These  were  raised  in  the  usual  manner,  with  the  following  result. 
I  should  state  that  there  were  originally  eight  plants  on  each 
side;  but  as  two  of  the  self-fertilised  became  extremely  un- 
healthy and  never  grew  to  near  their  full  height,  these  as  well 
as  their  opponents  have  been  struck  out  of  the  list.  If  they  had 
been  retained,  they  would  have  made  the  average  height  of  the 
crossed  plants  unfairly  greater- than  that  of  the  self-fertilised. 
I  have  acted  in  the  same  manner  in  a  few  other  instances,  when 
one  of  a  pair  plainly  became  very  unhealthy. 

Table  VII-  (Sixth  Generation.") 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
93 
91 

Inches. 
50 1 
65 

II. 

79 
86  £ 
88 

50 
87 
62 

III. 

87  J 

64  J 

Total  inches. 

525 

379 

The  average  height  of  the  six  crossed  plants  is  here  87*5,  and 
of  the  six  self-fertilised  plants  63  ■  16,  or  as  100  to  72.  This  large 
difference  was  chiefly  due  to  most  of  the  plants,  especially  the 


Chap.  II.    CKOSSED  AND   SELF-FEKTILISED   PLANTS.        37 


self-fertilised  ones,  having  become  unhealthy  towards  the  close 
of  their  growth,  and  they  were  severely  attacked  by  aphides. 
From  this  cause  nothing  can  be  inferred  with  respect  to  their 
relative  fertility.  In  this  generation  we  have  the  first  instance 
of  a  self-fertilised  plant  in  Pot  II.  exceeding  (though  only  by 
half  an  inch)  its  crossed  opponent.  This  victory  was  fairly  won 
after  a  long  struggle.  At  first  the  self-fertilised  plant  was  several 
inches  taller  than  its  opponent,  but  when  the  latter  was  M 
feet  high  it  had  grown  equal ;  it  then  grew  a  little  taller  than 
the  self-fertilised  plant,  but  was  ultimately  beaten  by  it  to  the 
extent  of  half  an  inch,  as  shown  in  the  table.  I  was  so  much 
surprised  at  this  case  that  I  saved  the  self-fertilised  seeds  of 
this  plant,  which  I  will  call  the  "  Hero,"  and  experimented  on 
its  descendants,  as  will  hereafter  be  described. 

Besides  the  plants  included  in  Table  VII.,  nine  crossed  and 
nine  self-fertilised  plants  of  the  same  lot  were  raised  in  two 
other  pots,  IV.  and  V.  These  pots  had  been  kept  in  the  hot- 
house, but  from  want  of  room  were,  whilst  the  plants  were 
young,  suddenly  moved  during  very  cold  weather  into  the 
coldest  part  of  the  greenhouse.  They  all  suffered  greatly,  and 
never  quite  recovered.  After  a  fortnight  only  two  of  the  nine 
self-fertilised  seedlings  were  alive,  whilst  seven  of  the  crossed 
survived.  The  tallest  of  these  latter  plants  when  measured  was 
47  inches  in  height,  whilst  the  tallest  of  the  two  surviving  self- 
fertilised  plants  was  only  32  inches.  Here  again  we  see  how  much 
more  vigorous  the  crossed  plants  are  than  the  self-fertilised. 

Crossed  and  self-fertilised  Plants  of  the  Seventh  Generation.-^ 
These  were  raised  as  heretofore  with  the  following  result : — ■ 

Table  VIII.  (Seventh  Generation.) 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 

84  § 
76§ 

Inches. 
74 1 
84 
55* 

II. 

84| 

90 

82§ 

65 
51| 

80§ 

III. 

83 
86 

67 1 
60§ 

IV. 

84§ 

75§ 

Total  inches. 

755-50 

614-25 

• 

38  IPOMCEA  PUEPUEEA.  Chap.  II. 

Each  of  these  nine  crossed  plants  is  higher  than  its  opponent, 
though  in  one  case  only  by  three-quarters  of  an  inch.  Their 
average  height  is  83 '  94  inches,  and  that  of  the  self-fertilised 
plants  68*25,  or  as  100  to  81.  These  plants,  after  growing  to 
their  full  height,  became  very  unhealthy  and  infested  with 
aphides,  just  when  the  seeds  were  setting,  so  that  many  of  the 
capsules  failed,  and  nothing  can  be  said  on  their  relative 
fertility. 

Crossed  and  self-fertilised  Plants  of  the  Eighth  Generation. — As 
just  stated,  the  plants  of  the  last  generation,  from  which  the 
present  ones  were  raised,  were  very  unhealthy  and  their  seeds 
of  unusually  small  size ;  and  this  probably  accounts  for  the  two 
lots  behaving  differently  to  what  they  did  in  any  of  the  pre- 
vious or  succeeding  generations.  Many  of  the  self- fertilised 
seeds  germinated  before  the  crossed  ones,  and  these  were  of 
course  rejected.  When  the  crossed  seedlings  in  Table  IX.  had 
grown  to  a  height  of  between  1  and  2  feet,  they  were  all,  or 
almost  all,  shorter  than  their  self-fertilised  opponents,  but  were 
not  then  measured.  When  they  had  acquired  an  average  height 
of  32 '  28  inches,  that  of  the  self-fertilised  plants  was  40  ■  68,  or 
as  100  to  122.  Moreover,  every  one  of  the  self-fertilised  plants, 
with  a  single  exception,  exceeded  its  crossed  opponent.  When, 
however,  the  crossed  plants  had  grown  to  an  average  height  of 
77  *  56  inches,  they  just  exceeded  (viz.,  by  •  7  of  an  inch)  the 
average  height  of  the  self-fertilised  plants ;  but  two  of  the  latter 
were  still  taller  than  their  crossed  opponents.  I  was  so  much 
astonished  at  this  whole  case,  that  I  tied  string  to  the  summits 
of  the  rods  ;  the  plants  being  thus  allowed  to  continue  climbing 
upwards.  When  their  growth  was  complete  they  were  un- 
twined, stretched  straight,  and  measured.  The  crossed  plants 
had  now  almost  regained  their  accustomed  superiority,  as  may 
be  seen  in  Table  IX. 

The  average  height  of  the  eight  crossed  plants  is  here  113  "25 
inches,  and  that  of  the  self-fertilised  plants  96-65,  or  as  100  to 
85.  Nevertheless  two  of  the  self-fertilised  plants,  as  may  be  seen 
in  the  table,  were  still  higher  than  their  crossed  opponents. 
The  latter  manifestly  had  much  thicker  stems  and  many  more 
lateral  branches,  and  looked  altogether  more  vigorous  than  the 
self-fertilised  plants,  and  generally  flowered  before  them.  The 
earlier  flowers  produced  by  these  self-fertilised  plants  did  not 
set  any  capsules,  and  their  anthers  contained  only  a  small 
amount  of  pollen ;  but  to  this  subject  I  shall  return.    Neverthe- 


Chap.  II.     CEOSSED   AND   SELF-FERTILISED   PLANTS. 


39 


less  capsules  produced  by  two  other  self-fertilised  plants  of  the 
same  lot,  not  included  in  Table  IX.,  which  had  been  highly 
favoured  by  being  grown  in  separate  pots,  contained  the  large 
average  number  of  5  *  1  seeds  per  capsule. 

Table  IX.  {Eighth  Generation.') 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
lllf 
127 
130  g 

Inches. 
96 
54 
93 1 

II. 

971 
89 1 

94 
125 1 

III. 

103 1 
lOOf 

147  | 

115| 

84 1 

109 1 

Total  inches. 

908-25 

773-25 

Crossed  and  self -fertilised  Plants  of  the  Ninth  Generation. — 
The  plants  of  this  generation  were  raised  in  the  same  maimer 
as  before,  with  the  result  shown  in  Table  X. : — 

The  fourteen  crossed  plants  average  in  height  81  ■  39  inches 
and  the  fourteen  self-fertilised  plants  64-07,  or  as  100  to  79. 
One  self-fertilised  plant  in  Pot  III.  exceeded,  and  one  in  Pot  IV. 
equalled  in  height,  its  opponent.  The  self-fertilised  plants 
showed  no  sign  of  inheriting  the  precocious  growth  of  their 
parents;  this  having  been  due,  as  it  would  appear,  to  the 
abnormal  state  of  the  seeds  from  the  unhealthiness  of  their 
parents.  The  fourteen  self-fertilised  plants  yielded  only  forty 
spontaneously  self-fertilised  capsules,  to  which  must  be  added 
seven,  the  product  of  ten  flowers  artificially  self-fertilised.  On 
the  other  hand,  the  fourteen  crossed  plants  yielded  152  spon- 
taneously self-fertilised  capsules ;  but  thirty-six  flowers  on  these 
plants  were  crossed  (yielding  thirty-three  capsules),  and  these 
flowers  would  probably  have  produced  about  thirty  sponta- 
neously self-fertilised  capsules.  Therefore  an  equal  number 
of  the  crossed  and  self-fertilised  plants  would  have  produced 
capsules  in  the  proportion  of  about  182  to  47,  or  as  100  to  26. 
Another  phenomenon  was  well  pronounced  in  this  generation, 
out  I  believe  had  occurred  previously  to  a  slight  extent ; 
3 


40 


IPOMCBA    PURPUREA.. 


Cray.  II 


namely,  that  most  of  the  flowers  on  the  self-fertilised  plants 
were  somewhat  monstrous.  The  monstrosity  consisted  in  the 
corolla  being  irregularly  split  so  that  it  did  not  open  properly, 
with  one  or  two  of  the  stamens  slightly  foliaceous,  coloured, 
and  firmly  coherent  to  the  corolla.  I  observed  this  monstrosity 
in  only  one  flower  on  the  crossed  plants.  The  self-fertilised 
plants,  if  well  nourished,  would  almost  certainly,  in  a  few  more 
generations,  have  produced  double  flowers,  for  they  had  already 
become  in  seme  degree  sterile.* 


Table  X.  (Ninth  Generation.) 

No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
83 1 
85| 
83 1 

Inches. 
57 
71 
48 1 

II. 

83  § 
64 1 
64| 

45 
43  f 
38| 

III. 

79 

88| 

61 

63 
71 

89 1 

IV. 

82  i 
90 

82 1 

76£ 

V. 

Crowded  plants. 

89 1 
92| 
92 1 

67 

74  § 
70 

Total  inches. 

1139-5 

897-0 

Crossed  and  self-fertilised  Plants  of  the  Tenth  Generation. — Six 
plants  were  raised  in  the  usual  manner  from  the  crossed  plants 
of  the  last  generation  (Table  X.)  again  intercrossed,  and  from 
the  self-fertilised  again  self-fertilised.  As  one  of  the  crossed 
plants  in  Pot  I.  in  the  following  table  became  much  diseased, 
having  crumpled  leaves,  and  producing  hardly  any  capsules,  it 
and  its  opponent  have  been  struck  out  of  the  table. 


*  See  on  this  subject '  Variation 
of   Animals    and    Plants    under 


Domestication,'  chap,   xviii.  2nd 
edit.  vol.  ii.  p.  152. 


Ceap.  II.      FLOWERS   ON   SAME    PLANT   CROSSED. 
Table  XI.  {Tenth  Generation.) 


41 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

1. 

Inches. 
92  § 
94 1 

Indies. 
47 1 
34§ 

II. 

87 
89 1 
105 

54| 
49f 
66 1 

Total  inches. 

468-5 

252-0 

The  five  crossed  plants  average  93  ■  7  inches,  and  the  five  self- 
fertilised  only  50-4,  or  as  100  to  54.  This  difference,  however, 
is  so  great  that  it  must  be  looked  at  as  in  part  accidental.  The 
six  crossed  plants  (the  diseased  one  here  included)  yielded  spon- 
taneously 101  capsules,  and  the  six  self-fertilised  plants  88, 
the  latter  being  chiefly  produced  by  one  of  the  plants.  But  as 
the  diseased  plant,  which  yielded  hardly  any  seed,  is  here  included, 
the  ratio  of  101  to  88  does  not  fairly  give  the  relative  fertility  of 
the  two  lots.  The  stems  of  the  six  crossed  plants  looked  so 
much  finer  than  those  of  the  six  self-fertilised  plants,  that  after 
the  capsules  had  been  gathered  and  most  of  the  leaves  had  fallen 
off,  they  were  weighed.  Those  of  the  crossed  plants  weighed 
2,693  grains,  whilst  those  of  the  self-fertilised  plants  weighed 
only  1,173  grains,  or  as  100  to  44;  but  as  the  diseased  and 
dwarfed  crossed  plant  is  here  included,  the  superiority  of  the 
former  in  weight  was  really  greater. 

The  Effects  on  the  Offspring  of  crossing  different  Flowers 
on  the  same  Plant,  instead  of  crossing  distinct  Individuals. 
— In  all  the  foregoing  experiments,  seedlings  from 
flowers  crossed  by  pollen  from  a  distinct  plant  (though 
in  the  later  generations  more  or  less  closely  related) 
were  put  into  competition  with,  and  almost  invariably 
proved  markedly  superior  in  height  to  the  offspring 
from  self-fertilised  flowers.  I  wished,  therefore,  to 
ascertain  whether  a  cross  between  two  flowers  on  the 
same  plant  would  give  to  the  offspring  any  superiority 


42  IPOMCEA   PURPUREA.  Chap.  II. 

over  the  offspring  from  flowers  fertilised  with  their 
own  pollen.  I  procured  some  fresh  seed  and  raised 
two  plants,  which  were  covered  with  a  net ;  and  several 
of  their  flowers  were  crossed  with  pollen  from  a  dis- 
tinct flower  on  the  same  plant.  Twenty-nine  capsules 
thus  produced  contained  on  an  average  4  ■  86  seeds  per 
capsule ;  and  100  of  these  seeds  weighed  36  •  77  grains. 
Several  other  flowers  were  fertilised  with  their  own 
pollen,  and  twenty-six  capsules  thus  produced  con- 
tained on  an  average  4*42  seeds  per  capsule;  100  of 
which  weighed  42  ■  61  grains.  So  that  a  cross  of  this 
kind  appears  to  have  increased  slightly  the  number  of 
seeds  per  capsule,  in  the  ratio  of  100  to  91 ;  but  these 
crossed  seeds  were  lighter  than  the  self-fertilised  in  the 
ratio  of  86  to  100.  I  doubt,  however,  from  other 
observations,  whether  these  results  are  fully  trust- 
worthy. The  two  lots  of  seeds,  after  germinating  on 
sand,  were  planted  in  pairs  on  the  opposite  sides  of  nine 
pots,  and  were  treated  in  every  respect  like  the  plants 
in  the  previous  experiments.  The  remaining  seeds, 
some  in  a  state  of  germination  and  some  not  so,  were 
sown  on  the  opposite  sides  of  a  large  pot  (No.  X.) ; 
and  the  four  tallest  plants  on  each  side  of  this  pot 
were  measured.  The  result  is  shown  in  the  following 
table  :— 

The  average  height  of  the  thirty-one  crossed  plants  is 
73  •  23  inches,  and  that  of  the  thirty-one  self-fertilised 
plants  77*41  inches;  or  as  100  to  106.  Looking  to 
each  pair,  it  may  be  seen  that  only  thirteen  of  the 
crossed  plants,  whilst  eighteen  of  the  self-fertilised 
plants  exceed  their  opponents.  A  record  was  kept  with 
respect  to  the  plant  which  flowered  first  in  each  pot ; 
and  only  two  of  the  crossed  flowered  before  one  of  the 
self-fertilised  in  the  same  pot ;  whilst  eight  of  the  self- 
fertilised  flowered   first.     It  thus    appears  that   the 


Chap.  II.     ELOWEKS   ON   SAME   PLANT   CEOSSED. 


43 


Table  XII. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

Inches. 

Inches. 

I. 

82 

77 1 

75 

87 

65 

64 

76 

87§ 

II. 

73  i 

84 

43 

86 1 

65| 

90 1 

III. 

61| 

86 

85 

69 j 

89 

87  i 

IV. 

83 

80 | 

73| 
67 

88 1 
84 1 

V. 

78 

661 

77 1 
81| 

76f 
57 

VI. 

70| 

80 

79 

82 1 

79| 

55 1 

VII. 

76 

77 

84 1 
79 

83| 
73 1 

VIII. 

73 

76  j 

67 

82 

83 

80 1 

IX. 

73| 

78 1 

78 

67 1 

xc 

34 

82  i 

Crowded  plants. 

82 

36 1 

84« 
71 

69| 

75f 

Total  inches. 

2270-25 

2399-75 

44  IPOMCEA  PURPUREA.  Chap.  II. 

crossed  plants  are  slightly  inferior  in  height  and  in 
earliness  of  flowering  to  the  self-fertilised.  But  the 
inferiority  in  height  is  so  small,  namely  as  100  to  106, 
that  I  should  have  felt  very  doubtful  on  this  head, 
had  I  not  cut  down  all  the  plants  (except  those 
in  the  crowded  pot  No.  X.)  close  to  the  ground  and 
weighed  them.  The  twenty -seven  crossed  plants 
weighed  16^  ounces,  and  the  twenty-seven  self-fer- 
tilised plants  20^  ounces;  and  this  gives  a  ratio  of 
100  to  124. 

A  self-fertilised  plant  of  the  same  parentage  as  those 
in  Table  XII.  had  been  raised  in  a  separate  pot  for  a 
distinct  purpose ;  and  it  proved  partially  sterile,  the 
anthers  containing  very  little  pollen.  Several  flowers 
on  this  plant  were  crossed  with  the  little  pollen  which 
could  be  obtained  from  the  other  flowers  on  the  same 
plant ;  and  other  flowers  were  self-fertilised.  From  the 
seeds  thus  produced  four  crossed  and  four  self-fertilised 
plants  were  raised,  which  were  planted  in  the  usual 
manner  on  the  opposite  sides  of  two  pots.  All  these 
four  crossed  plants  were  inferior  in  height  to  their 
opponents ;  they  averaged  78 '  18  inches,  whilst  the 
four  self- fertilised  plants  averaged  84  •  8  inches  ;  or  as 
100  to  108.*  This  case,  therefore,  confirms  the  last. 
Taking  all  the  evidence  together,  we  must  conclude 
that  these  strictly  self-fertilised  plants  grew  a  little 
taller,  were  heavier,  and  generally  flowered  before 
those  derived  from  a  cross  between  two  flowers  on  the 
same  plant.  These  latter  plants  thus  present  a  won- 
derful contrast  with  those  derived  from  a  cross  between 
two  distinct  individuals. 


*  From  one  of  these  self-ferti-  an   average  only  3*2  seeds  per 

lised  plants,    spontaneously  self-  capsule;   so  that  this  plant  had 

fertilised,  I  gathered  twenty-four  apparently  inherited  some  of  tho 

capsules,  and  they  contained  on  sterility  of  its  parent. 


Chap.  II.  CROSS  WITH  A  FRESH  STOCK.  45 

TJie  Effects  on  the  Offspring  of  a  Cross  with  a  distinct 
or  fresh  Stock  belonging:  to  the  same  Variety. — From  the 
two  foregoing  series  of  experiments  we  see,  firstly,  the 
good  effects  during  several  successive  generations  of 
a  cross  between  distinct  plants,  although  these  were 
in  some  degree  inter-related  and  had  been  grown 
under  nearly  the  same  conditions  ;  and,  secondly,  the 
absence  of  all  such  good  effects  from  a  cross  between 
flowers  on  the  same  plant ;  the  comparison  in  both 
cases  being  made  with  the  offspring  of  flowers  fertilised 
with  their  own  pollen.  The  experiments  now  to  be 
given  show  how  powerfully  and  beneficially  plants, 
which  have  been  intercrossed  during  many  successive 
generations,  having  been  kept  all  the  time  under 
nearly  uniform  conditions,  are  affected  by  a  cross  with 
another  plant  belonging  to  the  same  variety,  but  to  a 
distinct  family  or  stock,  which  had  grown  under  dif- 
ferent conditions. 

Several  flowers  on  the  crossed  plants  of  the  ninth  generation 
in  Table  X.,  were  crossed  with  pollen  from  another  crossed  plant 
of  the  same  lot.  The  seedlings  thus  raised  formed  the  tenth 
intercrossed  generation,  and  I  will  call  them  the  "  intercrossed 
plants."  Several  other  flowers  on  the  same  crossed  plants  of 
the  ninth  generation  were  fertilised  (not  having  been  castrated) 
with  pollen  taken  from  plants  of  the  same  variety,  but  belonging 
to  a  distinct  family,  which  had  been  grown  in  a  distant  garden 
at  Colchester,  and  therefore  under  somewhat  different  conditions. 
The  capsules  produced  by  this  cross  contained,  to  my  surprise, 
fewer  and  lighter  seeds  than  did  the  capsules  of  the  intercrossed 
plants ;  but  this,  I  think,  must  have  been  accidental.  The  seed- 
lings raised  from  them  I  will  call  the  "  Colchester-crossed."  The 
two  lots  of  seeds,  after  germinating  on  sand,  were  planted  in 
the  usual  manner  on  the  opposite  sides  of  five  pots,  and  the 
remaining  seeds,  whether  or  not  in  a  state  of  germination, 
were  thickly  sown  on  the  opposite  sides  of  a  very  large  pot, 
No.  VI.,  in  Table  XIII.  In  three  of  the  six  pots,  after  the 
young  plants  had  twined  a  short  way  up  their  sticks,  one  of  the 


46 


IPOMGEA  PUKPUEEA. 


Chap.  II 


Colchester-crossed  plants  was  much  taller  than  any  one  of 
the  intercrossed  plants  on  the  opposite  side  of  the  same  pot ; 
and  in  the  three  other  pots  somewhat  taller.  I  should  state 
that  two  of  the  Colchester-crossed  plants  in  Pot  IV.,  when 
about  two-thirds  grown,  became  much  diseased,  and  were, 
together  with  their  intercrossed  opponents,  rejected.  The 
remaining  nineteen  plants,  when  almost  fully  grown,  were 
measured,  with  the  following  result : — ■ 


Table  XIII. 


No.  of  Pot. 

Colchester-crossed 
Plants. 

Intercrossed  Plants  of 
the  Tenth  Generation. 

I. 

Inches. 
87 
87 1 
85 1 

Inches. 
78 
68 1 
94 1 

II. 

93| 

85 1 
90  g 

60 
87§ 
45 1 

III. 

84 1 
92| 
85 

70| 
81 1 
86f 

IV. 

95  f 

65| 

V. 

90 1 
86 1 
84 

85 1 

63 

62| 

VI. 

Crowded  plants  in  a 
very  large  pot. 

90| 

75 

71 

83 1 

63 

65 

43 1 

39| 

30| 

86 

53 

48| 

Total  inches. 

1596-50 

1249-75 

In  sixteen  out  of  these  nineteen  pairs,  the  Colchester-crossed 
plant  exceeded  in  height  its  intercrossed  opponent.  The  average 
height  of  the  Colchester-crossed  is  84 '03  inches,  and  that  of 
the  intercrossed  65  ■  78  inches ;  or  as  100  to  78.    With  respect 


Chap.  II.  DESCENDANTS   OP   HEEO.  47 

to  the  fertility  of  the  two  lots,  it  was  too  troublesome  to  collect 
and  count  the  capsules  on  all  the  plants ;  so  I  selected  two  of 
the  best  pots,  V.  and  VI.,  and  in  these  the  Colchester-crossed 
produced  269  mature  and  half-mature  capsules,  whilst  an  equal 
number  of  the  intercrossed  plants  produced  only  154  capsules ; 
or  as  100  to  57.  By  weight  the  capsules  from  the  Colchester- 
crossed  plants  were  to  those  from  the  intercrossed  plants  as 
100  to  51 ;  so  that  the  former  probably  contained  a  somewhat 
larger  average  number  of  seeds. 

We  learn  from  this  important  experiment  that 
plants  in  some  degree  related,  which  had  been  inter- 
crossed during  the  nine  previous  generations,  when  they 
were  fertilised  with  pollen  from  a  fresh  stock,  yielded 
seedlings  as  superior  to  the  seedlings  of  the  tenth 
intercrossed  generation,  as  these  latter  were  to  the  self- 
fertilised  plants  of  the  corresponding  generation.  For 
if  we  look  to  the  plants  of  the  ninth  generation  in 
Table  X.  (and  these  offer  in  most  respects  the  fairest 
standard  of  comparison)  we  find  that  the  intercrossed 
plants  were  in  height  to  the  self-fertilised  as  100  to  79, 
and  in  fertility  as  100  to  26  ;  whilst  the  Colchester- 
crossed  plants  are  in  height  to  the  intercrossed  as  100 
to  78,  and  in  fertility  as  100  to  51. 

The  Descendants  of  the  self-fertilised  Plant,  named  Hero,  which 
appeared  in  the  Sixth  self -fertilised  Generation. — In  the  five  genera- 
tions before  the  sixth,  the  crossed  plant  of  each  pair  was  taller 
than  its  self-fertilised  opponent ;  but  in  the  sixth  generation 
(Table  VII.,  Pot  II.)  the  Hero  appeared,  which  after  a  long  and 
dubious  struggle  conquered  its  crossed  opponent,  though  by 
only  half  an  inch.  I  was  so  much  surprised  at  this  fact,  that 
I  resolved  to  ascertain  whether  this  plant  would  transmit 
its  powers  of  growth  to  its  seedlings.  Several  flowers  on 
Hero  were  therefore  fertilised  with  their  own  pollen,  and  the 
seedlings  thus  raised  were  put  into  competition  with  self-fer- 
tilised and  intercrossed  plants  of  the  corresponding  generation. 
The  three  lots  of  seedlings  thus  all  belong  to  the  seventh  genera- 


48 


IPOMCEA  PURPUREA. 


Chap.  II 


tion.    Their  relative  heights  are  shown  in  the  twu  following 
iables : — 

Table  XIV. 


No.  of  Pot. 

Self-fertilised  Plants 
of  the  Seventh  Gene- 
ration, Children  of 
Hero. 

Self-fertilised  Plants 
of  the  Seventh  Gene- 
ration. 

I. 

Inches. 
74 
60 
55 1 

Inches. 
89 1 
61 
49 

II. 

92 
91  g 
74 1 

82 
56 
38 

Total  inches. 

447-25 

375-50 

The  average  height  of  the  six  self-fertilised  children  of  Hero 
is  74  "54  inches,  whilst  that  of  the  ordinary  self-fertilised  plants 
of  the  corresponding  generation  is  only  62  ■  58  inches,  or  as  100 
to  84. 

Table  XV. 


No.  of  Pot. 

Self-fertilised  Plants 
of  the  Seventh  Gene- 
ration, Children  of 
Hero. 

Intercrossed  Plants  of 
the  Seventh  Gene- 
ration. 

III. 

Inches. 
92 

Inches. 
76 1 

IV. 

87 
87 1 

89 
86 1 

Total  inches. 

266-75 

252-50 

Here  the  average  height  of  the  three  self-fertilised  children  of 
Hero  is  88-91  inches,  whilst  that  of  the  intercrossed  plants  is 
84-16;  or  as  100  to  95.  "We  thus  see  that  the  self-fertilised 
children  of  Hero  certainly  inherit  the  powers  of  growth  of  their 
parents;  for  they  greatly  exceed  in  height  the  self-fertilised 
offspring  of  the  other  self-fertilised  plants,  and  even  exceed 
by  a  trifle  the  intercrossed  plants, — all  of  the  corresponding 
generation. 


Chap.  II. 


DESCENDANTS   OP   HEEO. 


49 


Several  flowers  on  the  self-fertilised  children  of  Hero  in  Table 
XIV.  were  fertilised  with  pollen  from  the  same  flower ;  and  from 
the  seeds  thns  produced,  self-fertilised  plants  of  the  eighth 
generation  (grand-children  of  Hero)  were  raised.  Several  other 
flowers  on  the  same  plants  were  crossed  with  pollen  from  the  other 
children  of  Hero.  The  seedlings  raised  from  this  cross  may  be 
considered  as  the  offspring  of  the  union  of  brothers  and  sisters. 
The  result  of  the  competition  between  these  two  sets  of  seedlings 
(namely  self-fertilised  and  the  offspring  of  brothers  and  sisters) 
is  given  in  the  following  table : — 

Table  XVI. 


No.  of  Pot. 

Self-fertilised  Grand- 
children of  Hero, 
from  the  Self- fertilised 
Childri-n.     Eighth 
Generation. 

Grandchildren  from  a 
cross  between  the  self- 
fertilised  Children  of 
Hero.    Eighth  Gene- 
ration. 

I. 

Inches. 
86 1 
90 1 

Inches. 
95 1 
95jf 

11. 

96 

77  2 

85 
93 

III. 

73 

66 

84 1 

86 1 
82| 

70| 

IV. 

88£ 
84 
36 1 

74 

66 1 
15| 
38 
78| 

V. 

90 1 
90 1 

82 1 
83 1 

Total  inches. 

1037-00 

973-16 

The  average  height  of  the  thirteen  self-fertilised  grandchildren 
of  Hero  is  79 "  76  inches,  and  that  of  the  grandchildren  from  a 
cross  between  the  self-fertilised  children  is  74-85 ;  or  as  100  to  94. 
But  in  Pot  IV.  one  of  the  crossed  plants  grew  only  to  a  height  of 
15s  inches ;  and  if  this  plant  and  its  opponent  are  struck  out,  as 
would  be  the  fairest  plan,  the  average  height  of  the  crossed 
plants  exceeds  only  by  a  fraction  of  an  inch  that  of  the  self-ferti- 


50  IPOMCEA  PUBPUKEA.  Chap.  II, 

lised  plants.  It  is  therefore  clear  that  a  cross  between  the  self- 
fertilised  children  of  Hero  did  not  produce  any  beneficial  effect 
•worth  notice ;  and  it  is  very  doubtful  whether  this  negative  result 
can  be  attributed  merely  to  the  fact  of  brothers  and  sisters  having 
been  united,  for  the  ordinary  intercrossed  plants  of  the  several 
successive  generations  must  often  have  been  derived  \from  the 
union  of  brothers  and  sisters  (as  shown  in  Chap.  I.),  and  yet  all 
of  them  were  greatly  superior  to  the  self-fertilised  plants.  We 
are  therefore  driven  to  the  suspicion,  which  we  shall  soon  see 
strengthened,  that  Hero  transmitted  to  its  offspring  a  peculiar 
constitution  adapted  for  self-fertilisation. 

It  would  appear  that  the  self-fertilised  descendants  of  Hero 
have  not  only  inherited  from  Hero  a  power  of  growth  equal  to 
that  of  the  ordinary  intercrossed  plants,  but  have  become  more 
fertile  when  self-fertilised  than  is  usual  with  the  plants  of  the 
present  species.  The  flowers  on  the  self-fertilised  grandchildren 
of  Hero  in  Table  XVI.  (the  eighth  generation  of  self-fertilised 
plants)  were  fertilised  with  their  own  pollen  and  produced  plenty 
of  capsules,  ten  of  which  (though  this  is  too  few  a  number  for  a 
safe  average)  contained  5  ■  2  seeds  per  capsule, — a  higher  average 
than  was  observed  in  any  other  case  with  the  self-fertilised  plants. 
The  anthers  produced  by  these  self-fertilised  grandchildren  were 
also  as  well  developed  and  contained  as  much  pollen  as  those  on 
the  intercrossed  plants  of  the  corresponding  generation ;  whereas 
this  was  not  the  case  with  the  ordinary  self-fertilised  plants  of 
the  later  generations.  Nevertheless  some  few  of  the  flowers 
produced  by  the  grandchildren  of  Hero  were  slightly  monstrous, 
like  those  of  the  ordinary  self-fertilised  plants  of  the  later  genera- 
tions. In  order  not  to  recur  to  the  subject  of  fertility,  I  may  add 
that  twenty-one  self-fertilised  capsules,  spontaneously  produced 
by  the  great-grandchildren  of  Hero  (forming  the  ninth  generation 
of  self-fertilised  plants),  contained  on  an  average  4  -47  seeds ;  and 
this  is  as  high  an  average  as  the  self-fertilised  flowers  of  any 
generation  usually  yielded. 

Several  flowers  on  the  self-fertilised  grandchildren  of  Hero  in 
Table  XVI.  were  fertilised  with  pollen  from  the  same  flower ;  and 
the  seedlings  raised  from  them  (great-grandchildren  of  Hero) 
formed  the  ninth  self-fertilised  generation.  Several  other  flowers 
were  crossed  with  pollen  from  another  grandchild,  so  that  they 
may  be  considered  as  the  offspring  of  brothers  and  sisters,  and  the 
seedlings  thus  raised  may  be  called  the  intercrossed  great-grand- 
children.   And  lastly,  other  flowers  were  fertilised  with  pollen 


Chap.  II.  SUMMAKY   OF   OBSEEVATIONS.  51 

from  a  distinct  stock,  and  the  seedlings  thus  raised  may  be 
called  the  Colchester-crossed  great-grandchildren.  In  my  anxiety 
to  see  what  the  result  would  be,  I  unfortunately  planted  the 
three  lots  of  seeds  (after  they  had  germinated  on  sand)  in  the 
hothouse  in  the  middle  of  winter,  and  in  consequence  of  this  the 
seedlings  (twenty  in  number  of  each  kind)  became  very  unhealthy, 
some  growing  only  a  few  inches  in  height,  and  very  few  to  their 
proper  height.  The  result,  therefore,  cannot  be  fully  trusted ; 
and  it  would  be  useless  to  give  the  measurements  in  detail.  In 
order  to  strike  as  fair  an  average  as  possible,  I  first  excluded  all 
the  plants  under  50  inches  in  height,  thus  rejecting  all  the  most 
unhealthy  plants.  The  six  self-fertilised  thus  left  were  on  an 
average  66  ■  86  inches  high ;  the  eight  intercrossed  plants  63 '  2 
high;  and  the  seven  Colchester-crossed  65 "37  high;  so  that 
there  was  not  much  difference  between  the  three  sets,  the  self- 
fertilised  plants  having  a  slight  advantage.  Nor  was  there  any 
great  difference  When  only  the  plants  under  36  inches  in  height 
were  excluded.  Nor  again  when  all  the  plants,  however  much 
dwarfed  and  unhealthy,  were  included.  In  this  latter  case  the 
Colchester-crossed  gave  the  lowest  average  of  all ;  and  if  these 
plants  had  been  in  any  marked  manner  superior  to  the  other 
two  lots,  as  from  my  former  experience  I  fully  expected  they 
would  have  been,  I  cannot  but  think  that  some  vestige  of  such 
superiority  would  have  been  evident,  notwithstanding  the  very 
unhealthy  condition  of  most  of  the  plants.  No  advantage,  as  far 
as  we  can  judge,  was  derived  from  intercrossing  two  of  the 
grandchildren  of  Hero,  any  more  than  when  two  of  the  children 
were  crossed.  It  appears  therefore  that  Hero  and  its  descendants 
have  varied  from  the  common  type,  not  only  in  acquiring  great 
power  of  growth,  and  increased  fertility  when  subjected  to  self- 
fertilisation,  but  in  not  profiting  from  a  cross  with  a  distinct 
stock ;  and  this  latter  fact,  if  trustworthy,  is  a  unique  case,  as 
far  as  I  have  observed  in  all  my  experiments. 

Summary  on  the  Growth,  Vigour,  and  Fertility  of  the 
successive  Generations  of  the  crossed  and  self -fertilised 
Plants  of  Ipomoea  purpurea,  together  with  some  miscel- 
laneous Observations. 

In  the  following  table,  No.  XVII.,  we  see  the  average 
or'  mean  heights  of  the  ten  successive  generations  of 
the   intercrossed   and   self-fertilised  plants,  grown  in 


52 


IPOMCEA  PUEPUREA. 


Chap.  II 


competition  with,  each  other;  and  in  the  right-hand 
column  we  have  the  ratios  of  the  one  to  the  other,  the 
height  of  the  intercrossed  plants  being  taken  at  100. 
In  the  bottom  line  the  mean  height  of  the  seventy- 
three  intercrossed  plants  is  shown  to  be  85  ■  84  inches, 
and  that  of  the  seventy-three  self-fertilised  plants 
66  •  02  inches,  or  as  100  to  77. 

Table  XVII. 

Jpomoea  purpurea.     Summary  of  Measurements  (in  Inches)  of 
the  Ten  Generations. 


Number  of  the  Generation. 

Number 

of 
Crossed 
Plants. 

Average 
Height 

of  Crossed 
Plants. 

1 

Number 
,  of  Self- 
ferti- 
lised 
Plants. 

Average 
Height  of 
Self-ferti- 
lised 
Hants. 

Ratio  between 

Average 

Heights  of 

Crossed  and 

Self-fertilised 

Plants. 

First  generation  . 
Table  I. 

6 

86-00 

6     1   65-66 

as  100  to    76 

Second  generation 
Table  II. 

6 

84-16 

6 

66-33 

as  100  to  79 

Third  generation. 
Table  III. 

6 

77-41 

6 

52-83  las  100  to  68 

Fourth  generation     . 
Table  V. 

7 

69-78 

7 

60-14  las  100  to  86 

Fifth  generation  .      . 
Table  VI. 

6 

82-54 

6 

62-33 

as  100  to  75 

Sixth  generation . 
Table  VII. 

6 

87-50 

6 

63-16  !as  100  to  72 

I 

Seventh  generation   . 
Table  VIII. 

9 

83-94 

9 

68-25  las  100  to  81 

Eighth  generation     . 
Table  IX. 

8 

113-25 

8 

96-65 

as  100  to  85 

Ninth  generation 
Table  X. 

14 

81-39 

14 

64-07 

as  100  to  79 

Tenth  generation       . 
Table  XI. 

5 

93-70 

5 

50-40 

as  100  to  54 

All  the  ten  generations'! 
taken  together  .      ./ 

73 

85-84 

73 

60-02 

as  100  to  77 

Chap.  II.  SUMMARY   OF   OBSERVATIONS.  53 

The  mean  height  of  the  self-fertilised  plants  in 
each  of  the  ten  generations  is  also  shown  in  the 
accompanying  diagram,  that  of  the  intercrossed  plants 
being  taken  at  100 ;  and  on  the  right  side  we  see 
the  relative  heights  of  the  seventy-three  intercrossed 
plants,  and  of  the  seventy-three  self-fertilised  plants. 
The  difference  in  height  between  the    crossed   and 


&  a*  3m  2th  5th-  6th-  r*  aiA  a^icP1  Mcanofttieten 
Generation.  Ce/icrcUaivt 

Diagram  showing  the  mean  heights  of  the  crossed  and  self-fertilised 
plants  of  Ipomoea  purpurea  in  the  ten  generations;  the  mean  height  of  the 
crossed  plants  being  taken  as  100.  On  the  right  hand,  the  mean  heights  of 
the  crossed  and  self-fertilised  plants  of  all  the  generations  taken  together 
are  shown. 

self-fertilised  plants  will  perhaps  be  best  appreciated 
by  an  illustration :  If  all  the  men  in  a  country  were 
on  an  average  6  feet  high,  and  there  were  some  families 
which  had  been  long  and  closely  interbred,  these 
would  be  almost  dwarfs,  their  average  height  during 
ten  generations  being  only  4  feet  8£  inches. 


54  IPOMCEA  PUEPUREA.  Chap.  II 

It  should  be  especially  observed  that  the  average  dif- 
ference between  the  crossed  and  self-fertilised  plants 
is  not  due  to  a  few  of  the  former  having  grown  to  an 
extraordinary  height,  or  to  a  few  of  the  self-fertilised 
being  extremely  short,  but  to  all  the  crossed  plants 
having  surpassed  their  self-fertilised  opponents,  with 
the  few  following  exceptions.  The  first  occurred  in 
the  sixth  generation,  in  which  the  plant  named  "  Hero" 
appeared ;  two  in  the  eighth  generation,  but  the  self- 
fertilised  plants  in  this  generation  were  in  an  anomalous 
condition,  as  they  grew  at  first  at  an  unusual  rate  and 
conquered  for  a  time  the  opposed  crossed  plants  ;  and 
two  exceptions  in  the  ninth  generation,  though  one 
of  these  plants  only  equalled  its  crossed  opponent. 
Therefore,  of  the  seventy-three  crossed  plants,  sixty- 
eight  grew  to  a  greater  height  than  the  self-fertilised 
plants,  to  which  they  were  opposed. 

In  the  right-hand  column  of  figures,  the  difference 
in  height  between  the  crossed  and  self-fertilised  plants 
in  the  successive  generations  is  seen  to  fluctuate  much, 
as  might  indeed  have  been  expected  from  the  small 
number  of  plants  measured  in  each  generation  being 
insufficient  to  give  a  fair  average.  It  should  be 
remembered  that  the  absolute  height  of  the  plants 
goes  for  nothing,  as  each  pair  was  measured  as 
soon  as  one  of  them  had  twined  up  to  the  summit 
of  its  rod.  The  great  difference  in  the  tenth  genera- 
tion, viz.,  100  to  54,  no  doubt  was  partly  accidental, 
though,  when  these  plants  were  weighed,  the  differ- 
ence was  even  greater,  viz.,  100  to  44.  The  smallest 
amount  of  difference  occurred  in  the  fourth  and  the 
eighth  generations,  and  this  was  apparently  due  to 
both  the  crossed  and  self-fertilised  plants  having 
become  unhealthy,  which  prevented  the  former  attain- 
ing their  usual  degree  of  superiority.      This  was  an 


Chap.  II.  SUMMARY   OF   OBSERVATIONS.  55 

unfortunate  circumstance,  but  my  experiments  were 
not  thus  vitiated,  as  both  lots  of  plants  were  exposed 
to  the  same  conditions,  whether  favourable  or  un- 
favourable. 

There  is  reason  to  believe  that  the  flowers  of  this 
Ipomoea,  when  growing  out  of  doors,  are  habitually 
crossed  by  insects,  so  that  the  first  seedlings  which  I 
raised  from  purchased  seeds  were  probably  the  offspring 
of  a  cross.  I  infer  that  this  is  the  case,  firstly  from 
humble-bees  often  visiting  the  flowers,  and  from  the 
quantity  of  pollen  left  by  them  on  the  stigmas  of  such 
flowers  ;  and,  secondly,  from  the  plants  raised  from  the 
same  lot  of  seed  varying  greatly  in  the  colour  of  their 
flowers,  for  as  we  shall  hereafter  see,  this  indicates 
much  intercrossing.*  It  is,  therefore,  remarkable 
that  the  plants  raised  by  me  from  flowers  which  were, 
in  all  probability,  self-fertilised  for  the  first  time  after 
many  generations  of  crossing,  should  have  been  so 
markedly  inferior  in  height  to  the  intercrossed  plants 
as  they  were,  namely,  as  76  to  100.  As  the  plants 
which  were  self-fertilised  in  each  succeeding  generation 
necessarily  became  much  more  closely  interbred  in 
the  later  than  in  the  earlier  generations,  it  might  have 
been  expected  that  the  difference  in  height  between 
them  and  the  crossed  plants  would  have  gone  on  in- 
creasing ;  but,  so  far  is  this  from  being  the  case,  that 
the  difference  between  the  two  sets  of  plants  in  the 
seventh,  eighth,  and  ninth  generations  taken  together 
is  less  than  in  the  first  and  second  generations  together. 
When,  however,  we  remember  that  the  self-fertilised 
and  crossed  plants  are  all  descended  from  the  same 


*  Verlot  says  ('  Sur  la  Produc-  color,  cannot  be  kept  pure  unless 

tiou  des  Varietes,'  1865,   p.  66)  grown  at  a  distance  from  all  other 

that  certain  varieties  of  a  closely  varieties. 
allied  plant,  the  Convolvulus  tri- 


£>b  IPOMOEA  PUKPUKEA.  Chap.  IT. 

mother-plant,  that  many  of  the  crossed  plants  in  each 
generation  were  related,  often  closely  related,  and  that 
all  were  exposed  to  the  same  conditions,  which,  as  we 
shall  hereafter  find,  is  a  very  important  circumstance,  it 
is  not  at  all  surprising  that  the  difference  between 
them  should  have  somewhat  decreased  in  the  later 
generations.  It  is,  on  the  contrary,  an  astonishing  fact, 
that  the  crossed  plants  should  have  been  victorious, 
even  to  a  slight  degree,  over  the  self-fertilised  plants 
of  the  later  generations. 

The  much  greater  constitutional  vigour  of  the 
crossed  than  of -the  self-fertilised  plants,  was  proved  on 
five  occasions  in  various  ways ;  namely,  by  exposing 
them,  while  young,  to  a  low  temperature  or  to  a 
sudden  change  of  temperature,  or  by  growing  them, 
under  very  unfavourable  conditions,  in  competition 
with  full-grown  plants  of  other  kinds. 

With  respect  to  the  productiveness  of  the  crossed 
and  self-fertilised  plants  of  the  successive  generations, 
my  observations  unfortunately  were  not  made  on  any 
uniform  plan,  partly  from  the  want  of  time,  and  partly 
from  not  having  at  first  intended  to  observe  more  than 
a  single  generation.  A  summary  of  the  results  is  here 
given  in  a  tabulated  form,  the  fertility  of  the  crossed 
plants  being  taken  as  100. 

First  Generation  of  crossed  and  self  fertilised  Plants 
growing  in  competition  with  cne  another. — Sixty-five 
capsules  produced  from  flowers  on  five  crossed  plants 
fertilised  by  pollen  from  a  distinct  plant,  and  fifty-five 
capsules  produced  from  flowers  on  five  self-fertilised 
plants  fertilised  by  their  own  pollen,  contained  seeds 
in  the  proportion  of       .       .  .         .         .         .         .     100  to  93 

Fifty-six  spontaneously  self-fertilised  capsules  on 
the  above  five  crossed  plants,  and  twenty-five  sponta- 
neously self-fertilised  capsules  on  the  above  five  self- 
fertilised  plants,  yielded  seeds  in  the  proportion  of   .     100  to  99 


Chap.  II.  SUMMARY   OF    OBSERVATIONS.  57 

Combining  the  total  number  of  capsules  produced 
by  these  plants,  and  the  average  number  of  seeds  in 
each,  the  above  crossed  and  self-fertilised  plants 
yielded  seeds  in  the  proportion  of   .         .         .         .     100  to  64 

Other  plants  of  this  first  generation  grown  under 
unfavourable  conditions  and  spontaneously  self-ferti- 
lised, yielded  seeds  in  the  proportion  of  .         .         .     100  to  45 

Third  Generation  of  crossed  and  self-fertilised  Plants. 
— Crossed  capsules  compared  with  self-fertilised  cap- 
sules contained  seeds  in  the  ratio  of  100  to  94 

An  equal  number  of  crossed  and  self-fertilised 
plants,  both  spontaneously  self-fertilised,  produced 
capsules  in  the  ratio  of  .         .         .         .         .         .     100  to  38 

And  these  capsules  contained  seeds  in  the  ratio  of  .     100  to  94 

Combining  these  data,  the  productiveness  of  the 
crossed  to  the  self-fertilised  plants,  both  spontane- 
ously self-fertilised,  was  as 100  to  35 

Fourth  Generation  of  crossed  and  self-fertilised  Plants. 
— Capsules  from  flowers  on  the  crossed  plants  ferti- 
lised by  pollen  from  another  plant,  and  capsules  from 
flowers  on  the  self-fertilised  plants  fertilised  with  their 
own  pollen,  contained  seeds  in  the  proportion  of      .     100  to  94 

Fifth  Generation  of  crossed  and  self-fertilised  Plants. 
— The  crossed  plants  produced  spontaneously  a  vast 
number  more  pods  (not  actually  counted)  than  the 
selfrfertilised,  and  these  contained  seeds  in  the  pro- 
portion of     100  to  89 

Ninth  Generation  of  crossed  and  self-fertilised  Plants. 
— Fourteen  crossed  plants,  spontaneously  self-ferti- 
lised, and  fourteen  self-fertilised  plants  spontaneously 
self-fertilised,  yielded  capsules  (the  average  number 
of  seeds  per  capsule  not  having  been  ascertained)  in 
the  proportion  of  .  .....     100  to  26 

Plants  derived  from  a  cross  with  a  fresh  Stock  com- 
pared with  intercrossed  Plants. — The  offspring  of  inter- 
crossed plants  of  the  ninth  generation,  crossed  by  a 
fresh  stock,  compared  with  plants  of  the  same  stock 
intercrossed  during  ten  generations,  both  sets  of  plants 
left  uncovered  and  naturally  fertilised,  produced 
capsules  by  weight  as 100  to  51 

We  see  in  this  table  that   the  crossed  plants   are 


58  IPOMOEA  PURPUREA.  Chap.  II. 

always  in  some  degree  more  productive  than  the  self- 
fertilised  plants,  by  whatever  standard  they  are  com- 
pared. The  degree  differs  greatly;  but  this  depends 
chiefly  on  whether  an  average  was  taken  of  the  seeds 
alone,  or  of  the  capsules  alone,  or  of  both  combined. 
The  relative  superiority  of  the  crossed  plants  is  chiefly 
due  to  their  producing  a  much  greater  number  of  cap- 
sules, and  not  to  each  capsule  containing  a  larger 
average  number  of  seeds.  For  instance,  in  the  third 
generation  the  crossed  and  self-fertilised  plants  pro- 
duced capsules  in  the  ratio  of  100  to  38,  whilst  the 
seeds  in  the  capsules  on  the  crossed  plants  were  to 
those  on  the  self-fertilised  plants  only  as  100  to  94. 
In  the  eighth  generation  the  capsules  on  two  self- 
fertilised  plants  (not  included  in  the  above  table), 
grown  in  separate  pots  and  thus  not  subjected  to  any 
competition,  yielded  the  large  average  of  5'1  seeds. 
The  smaller  number  of  capsules  produced  by  the  self- 
fertilised  plants  may  be  in  part,  but  not  altogether, 
attributed  to  their  lessened  size  or  height ;  this  being 
chiefly  due  to  their  lessened  constitutional  vigour,  so 
that  they  were  not  able  to  compete  with  the  crossed 
plants  growing  in  the  same  pots.  The  seeds  produced 
by  the  crossed  flowers  on  the  crossed  plants  were  not 
always  heavier  than  the  self-fertilised  seeds  on  the 
self-fertilised  plants.  The  lighter  seeds,  whether  pro- 
duced from  crossed  or  self-fertilised  flowers,  generally 
germinated  before  the  heavier  seeds.  I  may  add  that 
the  crossed  plants,  with  very  few  exceptions,  flowered 
before  their  self-fertilised  opponents,  as  might  have 
been  expected  from  their  greater  height  and  vigour. 

The  impaired  fertility  of  the  self-fertilised  plants  was 
shown  in  another  way,  namely,  by  their  anthers  being 
smaller  than  those  in  the  flowers  on  the  crossed  plants. 
This  was  first  observed  in  the  seventh  generation,  but 


Chap.  II.  SUMMARY   OP   OBSERVATIONS.  59 

may  have  occurred  earlier.  Several  anthers  from  flowers 
on  the  crossed  and  self-fertilised  plants  of  the  eighth 
generation  were  compared  under  the  microscope  ;  and 
those  from  the  former  were  generally  longer  and  plainly 
broader  than  the  anthers  of  the  self-fertilised  plants. 
The  quantity  of  pollen  contained  in  one  of  the  latter 
was,  as  far  as  could  be  judged  by  the  eye,  about  half 
of  that  contained  in  one  from  a  crossed  plant.  The 
impaired  fertility  of  the  self-fertilised  plants  of  the 
eighth  generation  was  also  shown  in  another  manner, 
which  may  often  be  observed  in  hybrids — namely,  by  the 
first-formed  flowers  being  sterile.  For  instance,  the 
fifteen  first  flowers  on  a  self-fertilised  plant  of  one  of  the 
later  generations  were  carefully  fertilised  with  their 
own  pollen,  and  eight  of  them  dropped  off;  at  the  same 
time  fifteen  flowers  on  a  crossed  plant  growing  in  the 
same  pot  were  self-fertilised,  and  only  one  dropped  off. 
On  two  other  crossed  plants  of  the  same  generation, 
several  of  the  earliest  flowers  were  observed  to  fertilise 
themselves  and  to  produce  capsules.  In  the  plants  of 
the  ninth,  and  I  believe  of  some  previous  generations, 
very  many  of  the  flowers,  as  already  stated,  were 
slightly  monstrous ;  and  this  probably  was  connected 
with  their  lessened  fertility. 

All  the  self-fertilised  plants  of  the  seventh  genera- 
tion, and  I  believe  of  one  or  two  previous  generations, 
produced  flowers  of  exactly  the  same  tint,  namely,  of  a 
rich  dark  purple.  So  did  all  the  plants,  without  any 
exception,  in  the  three  succeeding  generations  of  self- 
fertilised  plants  ;  and  very  many  were  raised  on  account 
of  other  experiments  in  progress  not  here  recorded. 
My  attention  was  first  called  to  this  fact  by  my 
gardener  remarking  that  there  was  no  occasion  to  label 
the  self-fertilised  plants,  as  they  could  always  be  known 
by  their  colour.     The  flowers  were  as  uniform  in  tint 


60  IPOMCEA   PUKPUEEA.  Chap.  II. 

as  those  of  a  wild  species  growing  in  a  state  of  nature  ; 
whether  the  same  tint  occurred,  as  is  probable,  in  the 
earlier  generations,  neither  my  gardener  nor  self  could 
recollect.  The  flowers  on  the  plants  which  were  first 
raised  from  purchased  seed,  as  well  as  during  the  first 
few  generations,  varied  much  in  the  depth  of  the 
purple  tint ;  many  were  more  or  less  pink,  and  occa- 
sionally a  white  variety  appeared.  The  crossed  plants 
continued  to  the  tenth  generation  to  vary  in  the  same 
manner  as  before,  but  to  a  much  less  degree,  owing, 
probably,  to  their  having  become  more  or  less  closely 
inter-related.  We  must  therefore  attribute  the  extra- 
ordinary uniformity  of  colour  in  the  flowers  on  the 
plants  of  the  seventh  and  succeeding  self-fertilised 
generations,  to  inheritance  not  having  been  interfered 
with  by  crosses  during  several  preceding  generations, 
in  combination  with  the  conditions  of  life  having  been 
very  uniform. 

A  plant  appeared  in  the  sixth  self-fertilised  genera- 
tion, named  the  Hero,  which  exceeded  by  a  little  in 
height  its  crossed  antagonist,  and  which  transmitted 
its  powers  of  growth  and  increased  self-fertility  to  its 
children  and  grandchildren.  A  cross  between  the 
children  of  Hero  did  not  give  to  the  grandchildren 
any  advantage  over  the  self-fertilised  grandchildren 
raised  from  the  self-fertilised  children.  And  as  far  as 
my  observations  can  be  trusted,  which  were  made  on 
very  unhealthy  plants,  the  great-grandchildren  raised 
from  intercrossing  the  grandchildren  had  no  advantage 
over  the  seedlings  from  the  grandchildren  the  product 
of  continued  self-fertilisation;  and  what  is  far  more 
remarkable,  the  great-grandchildren  raised  by  crossing 
the  grandchildren  with  a  fresh  stock,  had  no  advantage 
over  either  the  intercrossed  or  self-fertilised  great- 
grandchildren     It  thus  appears   that  Hero  arid  its 


Chap.  II.  SUMMAKT   OF   OBSEKVATIONS.  61 

descendants  differed  in  constitution  in  an  extraordinary 
manner  from  ordinary  plants  of  the  present  species. 

Although  the  plants  raised  during  ten  successive 
generations  from  crosses  between  distinct  yet  inter- 
related plants  almost  invariably  exceeded  in  height, 
constitutional  vigour,  and  fertility  their  self-fertilised 
opponents,  it  has  been  proved  that  seedlings  raised 
by  intercrossing  flowers  on  the  same  plant  are  by  no 
means  superior,  on  the  contrary  are  somewhat  inferioi 
in  height  and  weight,  to  seedlings  raised  from  flowers 
fertilised  with  their  own  pollen.  This  is  a  remarkable 
fact,  which  seems  to  indicate  that  self-fertilisation  is 
in  some  manner  more  advantageous  than  crossing, 
unless  the  cross  brings  with  it,  as  is  generally  the  case, 
some  decided  and  preponderant  advantage ;  but  to  this 
subject  I  shall  recur  in  a  future  chapter. 

The  benefits  which  so  generally  follow  from  a 
cross  between  two  plants  apparently  depend  on  the 
two  differing  somewhat  in  constitution  or  character. 
This  is  shown  by  the  seedlings  from  the  intercrossed 
plants  of  the  ninth  generation,  when  crossed  with 
pollen  from  a  fresh  stock,  being  as  superior  in 
height  and  almost  as  superior  in  fertility  to  the  again 
intercrossed  plants,  as  these  latter  were  to  seedlings 
from  self-fertilised  plants  of  the  corresponding  gen- 
eration. We  thus  learn  the  important  fact  that  the 
mere  act  of  crossing  two  distinct  plants,  which  are 
in  some  degree  inter-related  and  which  have  been 
long  subjected  to  nearly  the  same  conditions,  does 
little  good  as  compared  with  that  from  a  cross  between 
plants  belonging  to  different  stocks  or  families,  and 
which  have  been  subjected  to  somewhat  different  con- 
ditions. We  may  attribute  the  good  derived  from 
the  crossing  of  the  intercrossed  plants  during  the 
ten  successive  generations  to  their  still  differing  some- 


62  IPOMCEA  PURPUREA.  Chap.  II 

what  in  constitution  or  character,  as  was  indeed  proved 
by  their  flowers  still  differing  somewhat  in  colour. 
But  the  several  conclusions  which  may  be  deduced 
from  the  experiments  on  Ipomoea  will  be  more  fully 
considered  in  the  final  chapters,  after  all  my  other 
observations  have  been  given. 


Chap.  HI.  MIMULUS  LUTEUS.  63 


CHAPTER  III. 

SCEOPHULAEIACE^S,   GeSNEEIACE^,    LABIATE,   ETO. 

Mimulus  luteus ;  height,  vigour,  and  fertility  of  the  crossed  and  self- 
fertilised  plants  of  the  first  four  generations — Appearance  of  a 
new,  tall,  and  higlily  self-fertile  variety — Offspring  from  a  cross 
between  self-fertilised  plants — Effects  of  a  cross  with  a  fresh  stock 
— Effects  of  crossing  flowers  on  the  same  plant — Summary  on 
Mimulus  luteus — Digitalis  purpurea,  superiority  of  the  crossed 
plants — Effects  of  crossing  flowers  on  the  same  plant — Calceolaria 
— Linaria  vulgaris  —  Verbascum  thapsus  —  Vandellia  nummulari- 
folia — Cleistogene  flowers — Gesneria  pendulina — Salvia  coccinea — 
Origanum  vulgare,  great  increase  of  the  crossed  plants  by  stolons 
— Thunbergia  alata. 

In  the  family  of  the  Scrophulariaceae  I  experimented 
on  species  in  the  six  following  genera:  Mimulus, 
Digitalis,  Calceolaria,  Linaria,  Verbascum,  and  Van- 
dellia. 

II.  SCEOPHULAEIACEiE.— Mimulus  luteus. 

The  plants  •which  I  raised  from  purchased  seed  varied  greatly 
in  the  colour  of  their  flowers,  so  that  hardly  two  individuals 
were  quite  alike;  the  corolla  being  of  all  shades  of  yellow, 
with  the  most  diversified  blotches  of  purple,  crimson,  orange, 
and  coppery  brown.  But  these  plants  differed  in  no  other 
respect.*  The  flowers  are  evidently  well  adapted  for  fertilisa- 
tion by  the  agency  of  insects ;  and  in  the  case  of  a  closely  allied 
species,  M.  rosea,  I  have  watched  bees  entering  the  flowers,  thus 
getting  their  backs  well  dusted  with  pollen;  and  when  they 
entered  another  flower  the  pollen  was  licked  off  their  backs  by 


*  I  sent  several  specimens  with      The  flowers  with  much  red  have 
variously  coloured  flowers  to  Kew,      been  named  by  horticulturists  as 
and  Dr.  Hooker  informs  me  that      var.  Youngiana. 
they   all    consisted  of  M.   luteus. 
4 


64  MIMULUS  LUTEUS.  Chap.  Ill, 

the  two-lipped  stigma,  the  lips  of  which  are  irritable  and  close 
like  a  forceps  on  the  pollen-grains.  If  no  pollen  is  enclosed 
between  the  lips,  these  open  again  after  a  time.  Mr.  Kitchener 
has  ingeniously  explained  *  the  use  of  these  movements,  namely, 
to  prevent  the  self-fertilisation  of  the  flower.  If  a  bee  with 
no  pollen  on  its  back  enters  a  flower  it  touches  the  stigma, 
which  quickly  closes,  and  when  the  bee  retires  dusted  with 
pollen,  it  can  leave  none  on  the  stigma  of  the  same  flower. 
But  as  soon  as  it  enters  any  other  flower,  plenty  of  pollen  is 
left  on  the  stigma,  which  will  be  thus  cross-fertibised.  Never- 
theless, if  insects  are  excluded,  the  flowers  fertilise  themselves 
perfectly  and  produce  plenty  of  seed ;  but  I  did  not  ascertain 
whether  this  is  effected  by  the  stamens  increasing  in  length 
with  advancing  age,  or  by  the  bending  down  of  the  pistil.  The 
chief  interest  in  my  experiments  on  the  present  species,  lies  in 
the  appearance  in  the  fourth  self-fertilised  generation  of  a 
variety  which  bore  large  peculiarly -coloured  flowers,  and  grew 
to  a  greater  height  than  the  other  varieties ;  it  likewise  became 
more  highly  self-fertile,  so  that  this  variety  resembles  the 
plant  named  Hero,  which  appeared  in  the  sixth  self-fertilised 
generation  of  Ipomcea. 

Some  flowers  on  one  of  the  plants  raised  from  the  purchased 
seeds  were  fertilised  with  their  own  pollen ;  and  others  on  the 
same  plant  were  crossed  with  pollen  from  a  distinct  plant.  The 
seeds  from  twelve  capsules  thus  produced  were  placed  in 
separate  watch-glasses  for  comparison ;  and  those  from  the  six 
crossed  capsules  appeared  to  the  eye  hardly  more  numerous 
than  those  from  the  six  self-fertilised  capsules.  But  when  the 
seeds  were  weighed,  those  from  the  crossed  capsules  amounted 
to  1-02  grain,  whilst  those  from  the  self-fertilised  capsules 
were  only  *  81  grain ;  so  that  the  former  were  either  heavier  or 
more  numerous  than  the  latter,  in  the  ratio  of  100  to  79. 

Crossed  and  self-fertilised  Plants  of  the  First  Generation. — Having 
ascertained,  by  leaving  crossed  and  self-fertilised  seed  on  damp 
sand,  that  they  germinated  simultaneously,  both  kinds  were 
thickly  sown  on  opposite  sides  of  a  broad  and  rather  shallow 
pan ;  so  that  the  two  sets  of  seedlings,  which  came  up  at  the 
same  time,  were  subjected  to  the  same  unfavourable  conditions. 
This  was  a  bad  method  of  treatment,  but  this  species  was  one  of 
the  first  on  which  I  experimented.    When  the  crossed  seedlinga 


'A  Year's  Botany,'  1874,  p.  118. 


Chap.  III.  CEOSSED   AND   SELF-FEKTILISED   PLANTS.        65 

were  on  an  average  half  an  inch  high,  the  self-fertilised  ones 
were  only  a  quarter  of  an  inch  high.  When  grown  to  their  full 
height  under  the  above  unfavourable  conditions,  the  four  tallest 
crossed  plants  averaged  7*62,  and  the  four  tallest  self-fertilised 
5  •  87  inches  in  height ;  or  as  100  to  77.  Ten  flowers  on  the  crossed 
plants  were  fully  expanded  before  one  on  the  self-fertilised 
plants.  A  few  of  these  plants  of  both  lots  were  transplanted 
into  a  large  pot  with  plenty  of  good  earth,  and  the  self-fertilised 
plants,  not  now  being  subjected  to  severe  competition,  grew 
during  the  following  year  as  tall  as  the  crossed  plants;  but 
from  a  case  which  follows  it  is  doubtful  whether  they  would 
have  long  continued  equal.  Some  flowers  on  the  crossed  plants 
were  crossed  with  pollen  from  another  plant,  and  the  capsules 
thus  produced  contained  a  rather  greater  weight  of  seed  than 
those  on  the  self-fertilised  plants  again  self-fertilised. 

Crossed  and  self -fertilised  Plants  of  the  Second  Generation. — Seeds 
from  the  foregoing  plants,  fertilised  in  the  manner  just  stated, 
were  sown  on  the  opposite  sides  of  a  small  pot  (I.)  and  came  up 
crowded.  The  four  tallest  crossed  seedlings,  at  the  time  of 
flowering,  averaged  8  inches  in  height,  whilst  the  four  tallest 
self-fertilised  plants  averaged  only  4  inches.  Crossed  seeds 
were  sown  by  themselves  in  a  second  small  pot,  and  self- 
fertilised  seeds  were  sown  by  themselves  in  a  third  small  pot 
so  that  there  was  no  competition  whatever  between  these  two 
lots.  Nevertheless  the  crossed  plants  grew  from  1  to  2 
inches  higher  on  an  average  than  the  self-fertilised.  Both  lots 
looked  equally  vigorous,  but  the  crossed  plants  flowered  earlier 
and  more  profusely  than  the  self-fertilised.  In  Pot  I.,  in  which 
the  two  lots  competed  with  each  other,  the  crossed  plants  flowered 
first  and  produced  a  large  number  of  capsules,  whilst  the 
self-fertilised  produced  only  nineteen.  The  contents  of  twelve 
capsules  from  the  crossed  flowers  on  the  crossed  plants,  and 
of  twelve  capsules  from  self-fertilised  flowers  on  the  self-fertilised 
plants,  were  placed  in  separate  watch-glasses  for  comparison ; 
and  the  crossed  seeds  seemed  more  numerous  by  half  than  the 
self-fertilised. 

The  plants  on  both  sides  of  Pot  I.,  after  they  had  seeded, 
were  cut  down  and  transplanted  into  a  large  pot  with  plenty  of 
good  earth,  and  on  the  following  spring,  when  they  had  grown 
to  a  height  of  between  5  and  6  inches,  the  two  lots  were  equal, 
as  occurred  in  a  similar  experiment  in  the  last  generation. 
But  after  some  weeks  the  crossed  plants  exceeded  the  self- 


66  MIMULUS  LUTEUS.         Chap.  Ill, 

fertilised  ones  on  the  opposite  side  of  the  same  pot,  though,  not 
nearly  to  so  great  a  degree  as  before,  when  they  were  subjected 
to  very  severe  competition. 

Crossed  and  self-fertilised  Plants  of  the  Third  Generation. — 
Crossed  seeds  from  the  crossed  plants,  and  self-fertilised  seeds 
from  the  self-fertilised  plants  of  the  last  generation,  were  sown 
thickly  on  opposite  sides  of  a  small  pot,  No.  I.  The  two  tallest 
plants  on  each  side  were  measured  after  they  had  flowered,  and 
the  two  crossed  ones  were  12  and  7i  inches,  and  the  two  self- 
fertilised  ones  8  and  5i  inches  in  height ;  that  is,  in  the  ratio  of 
100  to  69.  Twenty  flowers  on  the  crossed  plants  were  again 
crossed  and  produced  twenty  capsules ;  ten  of  which  contained 
1*33  grain  weight  of  seeds.  Thirty  flowers  on  the  self-fertilised 
plants  were  again  self-fertilised  and  produced  twenty-six 
capsules ;  ten  of  the  best  of  which  (many  being  very  poor)  con- 
tained only  •  87  grain  weight  of  seeds ;  that  is,  in  the  ratio  of 
100  to  65  by  weight. 

The  superiority  of  the  crossed  over  the  self-fertilised  id!  ants 
was  proved  in  various  ways.  Self-fertilised  seeds  were  sown  on 
one  side  of  a  pot,  and  two  days  afterwards  crossed  seeds  on  the 
opposite  side.  The  two  lots  of  seedlings  were  equal  until  they 
were  above  half  an  inch  high ;  but  when  fully  grown  the  two 
tallest  crossed  plants  attained  a  height  of  12  2  and  81  inches, 
whilst  the  two  tallest  self-fertilised  plants  were  only  8  and  5 1 
inches  high. 

In  a  third  pot,  crossed  seeds  were  sown  four  days  after  the 
self-fertilised,  and  the  seedlings  from  the  latter  had  at  first,  as 
might  have  been  expected,  an  advantage;  but  when  the  two 
lots  were  between  5  and  6  inches  in  height,  they  were  equal, 
and  ultimately  the  three  tallest  crossed  plants  were  11, 10,  and 
8  inches,  whilst  the  three  tallest  self-fertilised  were  12,  8h,  and 
7s  inches  in  height.  So  that  there  was  not  much  difference 
between  them,  the  crossed  plants  having  an  average  advantage 
of  only  the  third  of  an  inch.  The  plants  were  cut  down,  and 
without  being  disturbed  were  transplanted  into  a  larger  pot. 
Thus  the  two  lots  started  fair  on  the  following  spring,  and  now 
the  crossed  plants  showed  their  inherent  superiority,  for  the  two 
tallest  were  13  inches,  whilst  the  two  tallest  self-fertilised  plants 
were  only  11  and  81  inches  in  height ;  or  as  100  to  75.  The 
two  lots  were  allowed  to  fertilise  themselves  spontaneously :  the 
crossed  plants  produced  a  large  number  of  capsules,  whilst  the 
self-fertilised  produced  very  few  and  poor  ones.    The  seeds 


Chap.  III.  CROSSED   AND   SELF-FERTILISED   PLANTS.         67 

from  eight  of  the  capsules  on  the  crossed  plants  weighed  '  65 
grain,  whilst  those  from  eight  of  the  capsules  on  the  self-fer- 
tilised plants  weighed  only  ■  22  grain ;  or  as  100  to  34. 

The  crossed  plants  in  the  above  three  pots,  as  in  almost  all 
the  previous  experiments,  flowered  before  the  self-fertilised. 
This  occurred  even  in  the  third  pot  in  which  the  crossed  seeds 
were  sown  four  days  after  the  self-fertilised  seeds. 

Lastly,  seeds  of  both  lots  were  sown  on  opposite  sides  of  a 
large  pot  in  which  a  Fuchsia  had  long  been  growing,  so  that  the 
earth  was  full  of  roots.  Both  lots  grew  miserably;  but  the 
crossed  seedlings  had  an  advantage  at  all  times,  and  ultimately 
attained  to  a  height  of  Sh  inches,  whilst  the  self-fertilised  seed- 
lings never  exceeded  1  inch.  The  several  foregoing  experiments 
prove  in  a  decisive  manner  the  superiority  in  constitutional 
vigour  of  the  crossed  over  the  self-fertilised  plants. 

In  the  three  generations  now  described  and  taken  together,  the 
average  height  of  the  ten  tallest  crossed  plants  was  8 '  19  inches, 
and  that  of  the  ten  tallest  self-fertilised  plants  5 '  29  inches  (the 
plants  having  been  grown  in  small  pots),  or  as  100  to  65. 

In  the  next  or  fourth  self-fertilised  generation,  several  plants 
of  a  new  and  tall  variety  appeared,  which  increased  in  the 
later  self-fertilised  generations,  owing  to  its  great  self-fertility, 
to  the  complete  exclusion  of  the  original  kinds.  The  samo 
variety  also  appeared  amongst  the  crossed  plants,  but  as  it  was 
not  at  first  regarded  with  any  particular  attention,  I  know 
not  how  far  it  was  used  for  raising  the  intercrossed  plants  ;  and 
in  the  later  crossed  generations  it  was  rarely  present.  Owing  to 
the  appearance  of  this  tall  variety,  the  comparison  of  the  crossed 
and  self-fertilised  plants  of  the  fifth  and  succeeding  generations 
was  rendered  unfair,  as  all  the  self-fertilised  and  only  a  few  or 
none  of  the  crossed  plants  consisted  of  it.  Nevertheless,  the 
results  of  the  later  experiments  are  in  some  respects  well  worth 
giving. 

Crossed  and  self-fertilised  Plants  of  the  Fourth  Generation. — Seeds 
of  the  two  kinds,  produced  in  the  usual  way  from  the  two  sets  of 
plants  of  the  third  generation,  were  sown  on  opposite  sides  of 
two  pots  (I.  and  II.);  but  the  seedlings  were  not  thinned 
enough  and  did  not  grow  well.  Many  of  the  self-fertilised 
plants,  especially  in  one  of  the  pots,  consisted  of  the  new  and 
tall  variety  above  referred  to,  which  bore  large  and  almost  white 
flowers  marked  with  crimson  blotches.  I  will  call  it  the 
White  variety.    I  believe  that  it  first  appeared  amongst  both  the 


68  MIMULUS  LUTEUS.         Chap.  III. 

crossed  and  self-fertilised  plants  of  the  last  generation;  but 
neither  my  gardener  nor  myself  could  remember  any  such  variety 
in  the  seedlings  raised  from  the  purchased  seed.  It  must  there- 
fore have  arisen  either  through  ordinary  variation,  or,  judging 
from  its  appearance  amongst  both  the  crossed  and  self-fertilised 
plants,  more  probably  through  reversion  to  a  formerly  existing 
variety. 

In  Pot  I.  the  tallest  crossed  plant  was  84  inches,  and  the 
tallest  self-fertilised  5  inches  in  height.  In  Pot  II.  the  tallest 
crossed  plant  was  64  inches,  and  the  tallest  self-fertilised  plant, 
which  consisted  of  the  white  variety,  7  inches  in  height ;  and 
this  was  the  first  instance  in  my  experiments  on  Mimulus  in 
which  the  tallest  self-fertilised  plant  exceeded  the  tallest  crossed. 
Nevertheless,  the  two  tallest  crossed  plants  taken  together  were 
to  the  two  tallest  self-fertilised  plants  in  height  as  100  to  80. 
As  yet  the  crossed  plants  were  superior  to  the  self-fertilised  in 
fertility ;  for  twelve  flowers  on  the  crossed  plants  were  crossed 
and  yielded  ten  capsules,  the  seeds  of  which  weighed  1  ■  71  grain. 
Twenty  flowers  on  the  self-fertilised  plants  were  self-fertilised, 
and  produced  fifteen  capsules,  all  appearing  poor ;  and  the  seeds 
from  ten  of  them  weighed  only  "68  grain,  so  that  from  an 
equal  number  of  capsules  the  crossed  seeds  were  to  the  self- 
fertilised  in  weight  as  100  to  40. 

Grossed  and  self-fertilised  Plants  of  the  Fifth  Generation. — Seeds 
from  both  lots  of  the  fourth  generation,  fertilised  in  the  usual 
manner,  were  sown  on  opposite  sides  of  three  pots.  When  the 
seedlings  flowered,  most  of  the  self-fertilised  plants  were  found 
to  consist  of  the  tall  white  variety.  Several  of  the  crossed  plants 
in  Pot  I.  likewise  belonged  to  this  variety,  as  did  a  very  few  in 
Pots  II.  and  III.  The  tallest  crossed  plant  in  Pot  I.  was  7  inches, 
and  the  tallest  self-fertilised  plant  on  the  opposite  side  8  inches ; 
in  Pots  II.  and  III.  the  tallest  crossed  were  44  and  54,  and  the 
tallest  self-fertilised  7  and  64  inches  in  height;  so  that  the 
average  height  of  the  tallest  plants  in  the  two  lots  was  as  100 
for  the  crossed  to  126  for  the  self-fertilised ;  and  thus  we  have 
a  complete  reversal  of  what  occurred  in  the  four  previous  gene- 
rations. Nevertheless,  in  all  three  pots  the  crossed  plants 
retained  their  habit  of  flowering  before  the  self-fertilised.  The 
plants  were  unhealthy  from  being  crowded  and  from  the  extreme 
heat  of  the  season,  and  were  in  consequence  more  or  less 
sterile ;  but  the  crossed  plants  were  somewhat  less  sterile  than 
the  self-fertilised  plants. 


Chap.  III.   CEOSSED   AND   SELF-FERTILISED  PLANTS.        69 

Grossed  and  self-fertilised  Plan's  of  the  Sixth  Generation. — Seeds 
from  plants  of  the  fifth  generation  crossed  and  self-fertilised  in 
the  usual  manner  were  sown  on  opposite  sides  of  several  pots. 
On  the  self-fertilised  side  every  single  plant  belonged  to  the  tall 
white  variety.     On  the  crossed  side  some  plants  belonged  to  this 
variety,  but  the  greater  number  approached  in  character  to  the 
old  and  shorter  kinds  with  smaller  yellowish  flowers  blotched 
with  coppery  brown.    When  the  plants  on  both  sides  were  from  2 
to  3  inches  in  height  they  were  equal,  but  when  fully  grown 
the  self- fertilised  were  decidedly  the  tallest  and  finest  plants,  but, 
from  want  of  time,  they  were  not  actually  measured.    In  half 
the  pots  the  first  plant  which  flowered  was  a  self-fertilised  one, 
and  in  the  other  half  a  crossed  one.    And  now  another  remark- 
able change  was  clearly  perceived,  namely,  that  the  self-fertilised 
plants  had  become  more  self-fertile  than  the  crossed.    The 
pots  were  all  put  under  a  net  to  exclude  insects,  and  the  crossed 
plants  produced  spontaneously  only  fifty-five  capsules,  whilst 
the  self-fertilised  plants  produced  eighty-one  capsules,  or  as  100 
to  147.    The  seeds  from  nine  capsules  of  both  lots  were  placed 
in  separate  watch-glasses  for  comparison,  and  the  self-fertilised 
appeared  rather  the  more  numerous.     Besides  these  sponta- 
neously suit-fertilised  capsules,  twenty  flowers  on  the  crossed 
plants    again    crossed  yielded    sixteen    capsules;   twenty-five 
flowers  on  the  self-fertilised  plants  again  self-fertilised  yielded 
seventeen  capsules,  and  this  is  a  larger  proportional  number  of 
capsules  than  was  produced  by  the  self-fertilised  flowers  on  the 
self-fertilised  plants  in  the  previous  generations.    The  contents 
of  ten  capsules  of  both  these  lots  were  compared  in  separate 
watch-glasses,  and  the  seeds  from  the  self-fertilised  appeared 
decidedly  more  numerous  than  those  from  the  crossed  plants. 

Crossed  and  self-fertilised  Plants  of  the  Seventh  Generation. — 
Crossed  and  self-fertilised  seeds  from  the  crossed  and  self-ferti- 
lised plants  of  the  sixth  generation  were  sown  in  the  usual 
manner  on  opposite  sides  of  three  pots,  and  the  seedlings  were 
well  and  equally  thinned.  Every  one  of  the  self-fertilised  plants 
(and  many  were  raised)  in  this,  as  well  as  in  the  eighth  and  ninth 
generations,  belonged  to  the  tall  white  variety.  Their  uniformity 
of  character,  in  comparison  with  the  seedlings  first  raised  from 
the  purchased  seed,  was  quite  remarkable.  On  the  other  hand, 
the  crossed  plants  differed  much  in  the  tints  of  their  flowers, 
but  not,  I  think,  to  so  great  a  degree  as  those  first  raised. 
I  determined  this  time  to  measure  the  plants  on  both  sidoa 


70 


MIMULUS   LUTE  US. 


Chap.  III. 


carefully.  The  self-fertilised  seedlings  came  up  rather  before  the 
crossed,  but  both  lots  were  for  a  time  of  equal  height.  When  first 
measured,  the  average  height  of  the  six  tallest  crossed  plants  in 
the  three  pots  was  7 "  02,  and  that  of  the  six  tallest  self-fertilised 
plants  8*97  inches,  or  as  100  to  128.  When  fully  grown  the 
same  plants  were  again  measured,  with  the  result  shown  in  the 
following  table : — 

Taele  XVILI.  {Seventh  Generation.) 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
HI 
HI 

Inches. 
198 
18 

II. 

12 1 

112 

181 

14  f 

III. 

9| 

H8 

12f 
11 

Total  inches. 

68-63 

93-88 

The  average  height  of  the  six  crossed  is  here  11 '43,  and  that 
of  the  six  self-fertilised  15-64,  or  as  100  to  137. 

As  it  was  now  evident  that  the  tall  white  variety  transmitted 
its  characters  faithfully,  and  as  the  self-fertilised  plants  consisted 
exclusively  of  this  variety,  it  was  manifest  that  they  would 
always  exceed  in  height  the  crossed  plants  which  belonged 
chiefly  to  the  original  shorter  varieties.  This  line  of  experiment 
was  therefore  discontinued,  and  I  tried  whether  intercrossing 
two  self-fertilised  plants  of  the  sixth  generation,  growing  in  dis- 
tinct pots,  would  give  their  offspring  any  advantage  over  the 
offspring  of  flowers  on  one  of  the  same  plants  fertilised  with  their 
own  pollen.  These  latter  seedlings  formed  the  seventh  genera- 
tion of  self-fertilised  plants,  like  those  in  the  right-hand  column 
in  Table  XVIII. ;  the  crossed  plants  were  the  product  of  six 
previous  self-fertilised  generations  with  an  intercross  in  the 
last  generation.  The  seeds  were  allowed  to  germinate  on  sand, 
and  were  planted  in  pairs  on  opposite  sides  of  four  pots,  all  the 
remaining  seeds  being  sown  crowded  on  opposite  sides  of  Pot 
Y.  in  Table  XIX. ;  the  three  tallest  on  each  side  in  this  latter  pot 
being  alone  measured.  All  the  plants  were  twice  measured — the 
first  time  whilst  young,  and  the  average  height  of  the  crossed  plants 


CHAP.  III.    CROSSED   AND   SELF-FERTILISED   PLANTS.        71 

to  that  of  the  self-fertilised  was  then  as  100  to  122.    When  fully 
grown  they  were  again  measured,  as  in  the  following  table  : — 

Table  XIX. 


No.  of  Pot. 

Intercrossed  Plants 

from  Self-fertilised 

Plants  of  the  Sixth 

Generation. 

Self-fertilised  Plants 

of  the  Seventh 

Generation. 

I. 

Inches. 
12| 
10j 
10 
14§ 

Inches. 
15§ 

H| 

11 

11 

II. 

lOf 

n 

7 

HI 

HI 

8| 

14§ 

III. 

13| 

12 1 

10| 
ll6 

IV. 

71 

14( 

7 
8 

V. 

Crowded. 

8| 

9 

101 

Q2 

Total  in  inches. 

159-38 

175-50 

The  average  height  of  the  sixteen  intercrossed  plants  is  here 
9  •  96  inches,  and  that  of  the  sixteen  self-fertilised  plants  10  ■  96,  or 
as  100  to  110 ;  so  that  the  intercrossed  plants,  the  progenitors  oi 
which  had  been  self-fertilised  for  the  six  previous  generations, 
and  had  been  exposed  during  the  whole  time  to  remarkably  uni- 
form conditions,  were  somewhat  inferior  in  height  to  the  plants 
of  the  seventh  self-fertilised  generation.  But  as  we  shall  pre- 
sently see  that  a  similar  experiment  made  after  two  additional 
generations  of  self-fertilisation  gave  a  different  result,  I  know 
not  how  far  to  trust  the  present  one.  In  three  of  the  five 
pots  in  Table  XIX.  a  self-fertilised  plant  flowered  first,  and  in 
the  other  two  a  crossed  plant.  These  self-fertilised  plants  were 
remarkably  fertile,  for  twenty  flowers  fertilised  with  their  own 
pollen  produced  no  less  than  nineteen  very  fine  capsules  ! 


72  MIMULUS  LUTEUS.  Chap.  III. 

The  effects  of  a  Cross  with  a  distinct  Stock. — Some  flowers  on  the 
self-fertilised  plants  in  Pot  IV.  in  Table  XIX.  were  fertilised 
with  their  own  pollen,  and  plants  of  the  eighth  self-fertilised 
generation  were  thus  raised,  merely  to  serve  as  parents  in  the  fol- 
lowing experiment.  Several  flowers  on  these  plants  were  allowed 
to  fertilise  themselves  spontaneously  (insects  being  of  course 
excluded),  and  the  plants  raised  from  these  seeds  formed  the 
ninth  self-fertilised  generation ;  they  consisted  wholly  of  the  tall 
white  variety  with  crimson  blotches.  Other  flowers  on  the 
same  plants  of  the  eighth  self-fertilised  generation  were  crossed 
with  pollen  taken  from  another  plant  of  the  same  lot ;  so  that 
the  seedlings  thus  raised  were  the  offspring  of  eight  previous 
generations  of  self-fertilisation  with  an  intercross  in  the  last 
generation ;  these  I  will  call  the  intercrossed  plants.  Lastly, 
other  flowers  on  the  same  plants  of  the  eighth  self-fertilised 
generation  were  crossed  with  pollen  taken  from  plants  which  had 
been  raised  from  seed  procured  from  a  garden  at  Chelsea.  The 
Chelsea  plants  bore  yellow  flowers  blotched  with  red,  but  differed 
in  no  other  respect.  They  had  been  grown  out  of  doors,  whilst 
mine  had  been  cultivated  in  pots  in  the  greenhouse  for  the 
last  eight  generations,  and  in  a  different  kind  of  soil.  The 
seedlings  raised  from  this  cross  with  a  wholly  different  stock 
may  be  called  the  "  Chelsea-crossed."  The  three  lots  of  seeds 
thus  obtained  were  allowed  to  germinate  on  bare  sand;  and 
whenever  a  seed  in  all  three  lots,  or  in  only  two,  germinated  at 
the  same  time,  they  were  planted  in  pots  superficially  divided 
into  three  or  two  compartments.  The  remaining  seeds, 
whether  or  not  in  a  state  of  germination,  were  thickly  sown  in 
three  divisions  in  a  large  pot,  X.,  in  Table  XX.  When  the  plants 
had  grown  to  their  full  height  they  were  measured,  as  shown  in 
the  following  table ;  but  only  the  three  tallest  plants  in  each  of 
the  three  divisions  in  Pot  X.  were  measured. 

In  this  table  the  average  height  of  the  twenty-eight  Chelsea- 
crossed  plants  is  21  ■  62  inches ;  that  of  the  twenty-seven  inter- 
crossed plants  12*2;  and  that  of  the  nineteen  self-fertilised  10  •  44. 
But  with  respect  to  the  latter  it  will  be  the  fairest  plan  to  strike  out 
two  dwarfed  ones  (only  4  inches  in  height),  so  as  not  to  exaggerate 
the  inferiority  of  the  self-fertilised  plants;  and  this  will  raise  the 
average  height  of  the  seventeen  remaining  self-fertilised  plants 
to  11  •  2  inches.  Therefore  the  Chelsea-crossed  are  to  the  inter- 
crossed in  height  as  100  to  56 ;  the  Chelsea-crossed  to  the  self- 
fertilised  as  100  to  52 ;  and  the  intercrossed  to  the  self-fertilised 


Chap.  III.  CROSS  WITH  A  FRESH   STOCK. 

Table  XX. 


73 


No.  of  Pot. 

Plants  from  Self- 
fertilised  Plants  of 
the  Eighth  Genera- 
tion crossed  by 
Chelsea  Plants. 

Plants  from  ar  Jn- 
tercioss  between 
the  Plants  of  the 
Eighth  Self-ferti- 
lised Generation. 

I 
Self-fertilised 
Plants  of  the  Ninth 
Generation  from 

Plants  of  the 
Eighth  Self-ferti- 
lised Generation. 

I. 

Inches. 
30 1 
28  g 

Inches. 
14 
13  f 
13? 

Inches. 

10 1 
10 

II. 

20 1 
22 1 

HI 
12 

111 

12| 

HI. 

23f 
24 1 
25 1 

121 

8| 
HI 

6? 

IV. 

22| 

22 

17 

88 

4 

13! 
11 

V. 

22 1 
19£ 
23 1 

9 
11 

41 

13 
13 1 

VI. 

28| 
22 

18| 

7 

12| 

12 
16* 

VII. 

12| 

24| 
20| 
26 1 

15 

12§ 

H| 
15| 

•• 

VIH. 

17 1 
22| 

27 

13| 
14§ 
14| 

•• 

IX. 

22f 

6 
20§ 

HI 
17 

1*1 

•• 

X. 

Crowded  Plants. 

18 1 
16| 
17  | 

91 
10 

log 

H 

HI 

Total  inches. 

605-38 

329-50 

198-50 

74  MIMULTJS  LUTEUS.  Chap.  Ill, 

as  100  to  92.  W  e  thus  see  how  immensely  superior  in  height 
the  Chelsea-crossed  are  to  the  intercrossed  and  to  the  self- 
fertilised  plants.  They  began  to  show  their  superiority  when 
only  one  inch  high.  They  were  also,  when  fully  grown,  much 
more  branched  with  larger  leaves  and  somewhat  larger  flowers 
than  the  plants  of  the  other  two  lots,  so  that  if  they  had  been 
weighed,  the  ratio  would  certainly  have  been  much  higher  than 
that  of  100  to  56  and  52. 

The  intercrossed  plants  are  here  to  the  self-fertilised  in 
height  as  100  to  92;  whereas  in  the  analogous  experiment 
given  in  Table  XIX.  the  intercrossed  plants  from  the  self- 
fertilised  plants  of  the  sixth  generation  were  inferior  in  height 
to  the  self-fertilised  plants  in  the  ratio  of  100  to  110.  I 
doubt  whether  this  discordance  in  the  results  of  the  two 
experiments  can  be  explained  by  the  self-fertilised  plants  in  the 
present  case  having  been  raised  from  spontaneously  self- 
fertilised  seeds,  whereas  in  the  former  case  they  were  raised 
from  artificially  self-fertilised  seeds ;  nor  by  the  present  plants 
having  been  self-fertilised  during  two  additional  generations, 
though  this  is  a  more  probable  explanation. 

With  respect  to  fertility,  the  twenty-eight  Chelsea-crossed 
plants  produced  272  capsules;  the  twenty-seven  intercrossed 
plants  produced  24 ;  and  the  seventeen  self-fertilised  plants  17 
capsules.  All  the  plants  were  left  uncovered  so  as  to  be  naturally 
fertilised,  and  empty  capsules  were  rejected 

Capsules. 
Therefore  20  Chelsea-crossed  plants  would  have  produced  194*29 

„  i     20  Intercrossed  plants  „  „  17  ■  77 

„        20  Self-fertilised  plants  „  „  20  -00 

Grains. 
The  seeds  contained  in  8  capsules  from  the  Chelsea-  1   i .  i 

crossed  plants  weighed    .....         j 
The  seeds  contained  in  8  capsules  from  the  Intercrossed  )  n. k-i 

plants  weighed        ......        S 

The  seeds  contained  in  8  capsules  from  the  Self-fertilised  )  n .  33 

plants  weighed        ......         J 

If  we  combine  the  number  of  capsules  produced  together  with 
the  average  weight  of  contained  seeds,  we  get  the  following 
extraordinary  ratios : 

Weight  of  seed  produced  by  the  same  number  )         inn  t   4 
of  Chelsea-crossed  and  intercrossed  plants    .   ) 


Chap.  III.        FLOWERS   ON   SAME   PLANT   CROSSED.  75 

Weight  of  seed  produced  by  the  same  number  )  ,  ,,„  ,  „ 
of  Chelsea-crossed  and  self-fertilised  plants      J 

Weight  of  seeds  produced  by  the  same  number  )  q  1 00  to  73 
of  intercrossed  and  self-fertilised  plants    .    .    I 

It  is  also  a  remarkable  fact  that  the  Chelsea-crossed  plants 
exceeded  the  two  other  lots  in  hardiness,  as  greatly  as  they  did 
in  height,  luxuriance,  and  fertility.  In  the  early  autumn  most  of 
the  pots  were  bedded  out  in  the  open  ground ;  and  this  always 
injures  plants  which  have  been  long  kept  in  a  warm  greenhouse. 
All  three  lots  consequently  suffered  greatly,  but  the  Chelsea- 
crossed  plants  much  less  than  the  other  two  lots.  On  the  3rd  of 
October  the  Chelsea-crossed  plants  began  to  flower  again,  and 
continued  to  do  so  for  some  time ;  whilst  not  a  single  flower  was 
produced  by  the  plants  of  the  other  two  lots,  the  stems  of  which 
were  cut  almost  down  to  the  ground  and  seemed  half  dead. 
Early  in  December  there  was  a  sharp  frost,  and  the  stems  of 
Chelsea-crossed  were  now  cut  down ;  but  on  the  23rd  of  December 
they  began  to  shoot  up  again  from  the  roots,  whilst  all  the  plants 
of  the  other  two  lots  were  quite  dead. 

Although  several  of  the  self-fertilised  seeds,  from  which  the 
plants  in  the  right-hand  column  in  Table  XX.  were  raised,  germi- 
nated (and  were  of  course  rejected)  before  any  of  those  of  the 
other  two  lots,  yet  in  only  one  of  the  ten  pots  did  a  self- 
fertilised  plant  flower  before  the  Chelsea-crossed  or  the  inter- 
crossed plants  growing  in  the  same  pots.  The  plants  of  these 
two  latter  lots  flowered  at  the  same  time,  though  the  Chelsea- 
crossed  grew  so  much  taller  and  more  vigorously  than  the 
intercrossed. 

As  already  stated,  the  flowers  of  the  plants  originally  raised 
from  the  Chelsea  seeds  were  yellow ;  and  it  deserves  notice  that 
every  one  of  the  twenty-eight  seedlings  raised  from  the  tall 
white  variety  fertilised,  without  being  castrated,  with  pollen 
from  the  Chelsea  plants,  produced  yellow  flowers;  and  this 
shows  how  prepotent  this  colour,  which  is  the  natural  one  of 
the  species,  is  over  the  white  colour. 

The  Effects  on  the  Offspring  of  intercrossing  Flowers  on  the 
same  Plant,  instead  of  crossing  distinct  Individuals. — In  all  the 
foregoing  experiments  the  crossed  plants  were  the  product  of  a 
cross  between  distinct  plants.  I  now  selected  a  very  vigorous 
plant  in  Table  XX.,  raised  by  fertilising  a  plant  of  the  eighth 
self-fertilised  generation  with  pollen  from  the   Chelsea  stock. 


76 


MIMULUS  LUTEUS. 


Chap,  IH. 


Several  flowers  on  this  plant  were  crossed  with  pollen  from  other 
flowers  on  the  same  plant,  and  several  other  flowers  were 
fertilised  with  their  own  pollen.  Tho  seed  thus  produced  was 
allowed  to  germinate  on  bare  sand ;  and  the  seedlings  were 
planted  in  the  usual  manner  on  the  opposite  sides  of  six 
pots.  All  the  remaining  seeds,  whether  or  not  in  a  state  of 
germination,  were  sown  thickly  in  Pot  VII. ;  the  three  tallest 
plants  on  each  side  of  this  latter  pot  being  alone  measured.  As  I 
was  in  a  hurry  to  learn  the  result,  some  of  these  seeds  were  sown 
late  in  the  autumn,  but  the  plants  grew  so  irregularly  during 
the  winter,  that  one  crossed  plant  was  28?  inches,  and  two 
others  only  4,  or  less  than  4  inches  in  height,  as  may  be  seen 
in  Table  XXI.  Under  such  circumstances,  as  I  have  observed 
in  many  other  cases,  the  result  is  not  in  the  least  trust- 
worthy ;  nevertheless  I  feel  bound  to  give  the  measurements. 

Table  XXI. 


1 

No.  of  Pot. 

Plants  raised  from  a 
Cross  between  dif- 
ferent Flowers  on  the 
same  Plant. 

Plants  raised  from 

Flowers  fertilised 

with  their  own 

PoUen. 

I. 

Inches. 

17 

9 

Inches. 
17 
3J 

H. 

28§ 
16| 

13| 

19* 
6 
2 

III. 

4 
21 

15S 

io8 

IV. 

23| 
15§ 

<5§ 

V. 

7 

13| 

VI. 

18| 
ll8 

1! 
2 

VII. 
Crowded. 

21 

HI 
12| 

15J 

11 

llf 

Total  inches. 

210-88 

140-75 

Chap.  ILL       FLOWERS   ON   SAME   PLANT   CROSSED. 


77 


The  fifteen  crossed  plants  here  average  14*05,  and  the  fifteen 
self-fertilised  plants  9*38  in  height,  or  as  100  to  67.  But  if 
all  the  plants  under  ten  inches  in  height  are  struck  out,  the  ratio 
of  the  eleven  crossed  plants  to  the  eight  self-fertilised  plants 
is  as  100  to  82. 

On  the  following  spring,  some  remaining  seeds  of  the  two 
lots  were  treated  in  exactly  the  same  manner ;  and  the  measure- 
ments of  the  seedlings  are  given  in  the  following  table  :— 


Table  XXII. 


No.  of  Pot. 

Plants  raised  from  a 
Cross  between  diffe- 
rent Flowers  on  the 
same  Plant. 

Plants  raised  from 

Flowers  fertilised 

with  their  own  Pollen. 

I. 

Inches. 
15] 
12 

10* 

Inches. 

19  8 

20  § 
12f 

IL 

16 1 
13 1 

20 1 

11 1 
19| 
17 1 

in. 

181 

15 

131 

12§ 
15| 
17 

IV. 

19f 
19| 

16§ 
21§ 

v. 

25 1 

22| 

VI. 

15 

20 1 
27§ 

19| 
16§ 
19| 

VII. 

14 
13| 

76 
'8 
8 
7 

VIII. 
Crowded. 

18| 
18| 
18| 
18| 

20| 

17 1 
15| 
158 

Total  in  inches. 

370-88 

353-63 

78  MIMULUS   LUTEUS.  Chap.  Ill 

Here  the  average  height  of  the  twenty-two  crossed  plants  is 
16  "85,  and  that  of  the  twenty-two  self-fertilised  plants  16  "07  ;  or 
as  100  to  95.  But  if  four  of  the  plants  in  Pot  VII.,  which  are 
mnch  shorter  than  any  of  the  others,  are  struck  out  (and  this 
would  be  the  fairest  plan),  the  twenty-one  crossed  are  to  the 
nineteen  self-fertilised  plants  in  height  as  100  to  100 "  6 — that  is, 
are  equal.  All  the  plants,  except  the  crowded  ones  in  Pot  VIII., 
after  being  measured  were  cut  down,  and  the  eighteen  crossed 
plants  weighed  10  oz.,  whilst  the  same  number  of  self-fertilised 
plants  weighed  lOi  oz.,  or  as  100  to  102*5;  but  if  the  dwarfed 
plants  in  Pot  VII.  had  been  excluded,  the  self-fertilised  would 
have  exceeded  the  crossed  in  weight  in  a  higher  ratio.  In  all 
the  previous  experiments  in  which  seedlings  were  raised  from  a 
cross  between  distinct  plants,  and  were  put  into  competition 
with  self-fertilised  plants,  the  former  generally  flowered  first  ; 
but  in  the  present  case,  in  seven  out  of  the  eight  pots  a 
self-fertilised  plant  flowered  before  a  crossed  one  on  the 
opposite  side.  Considering  all  the  evidence  with  respect  to 
the  plants  in  Table  XXII.,  a  cross  between  two  flowers  on  th'e 
same  plant  seems  to  give  no  advantage  to  the  offspring  thus 
produced,  the  self-fertilised  plants  being  in  weight  superior.  But 
this  conclusion  cannot  be  absolutely  trusted,  owing  to  the 
measurements  given  in  Table  XXI.,  though  these  latter,  from 
the  cause  already  assigned,  are  very  much  less  trustworthy  than 
the  present  ones. 

Summary  of  Observations  on  Mimulus  luteus. — In  the 
three  first  generations  of  crossed  and  self-fertilised 
plants,  the  tallest  plants  alone  on  each  side  of  the 
several  pots  were  measured ;  and  the  average  height 
of  the  ten  crossed  to  that  of  the  ten  self-fertilised 
plants  was  as  100  to  64.  The  crossed  were  also  much 
more  fertile  than  the  self-fertilised,  and  so  much 
more  vigorous  that  they  exceeded  them  in  height,  even 
when  sown  on  the  opposite  side  of  the  same  pot  after 
an  interval  of  four  days.  The  same  superiority  was 
likewise  shown  in  a  remarkable  manner  when  both 
kinds  of  seeds  were  sown  on  the  opposite  sides  of  a  pot 
with  very  poor  earth  full  of  the  roots  of  another  plant. 


Chap.  III.  SUMMAEY   OF   OBSERVATIONS.  79 

In  one  instance  crossed  and  self-fertilised  seedlings, 
grown  in  rich  soil  and  not  put  into  competition  with 
each  other,  attained  to  an  equal  height.  When  we 
come  to  the  fourth  generation  the  two  tallest  crossed 
plants  taken  together  exceeded  by  only  a  little  the  two 
tallest  self-fertilised  plants,  and  one  of  the  latter  beat 
its  crossed  opponent, — a  circumstance  which  had  not 
occurred  in  the  previous  generations.  This  victorious 
self-fertilised  plant  consisted  of  a  new  white-flowered 
variety,  which  grew  taller  than  the  old  yellowish 
varieties.  From  the  first  it  seemed  to  be  rather  more 
fertile,  when  self-fertilised,  than  the  old  varieties,  and 
in  the  succeeding  self-fertilised  generations  became 
more  and  more  self-fertile.  In  the  sixth  generation  the 
self-fertilisecl  plants  of  this  variety  compared  with  the 
crossed  plants  produced  capsules  in  the  proportion 
of  147  to  100,  both  lots  being  allowed  to  fertilise 
themselves  spontaneously.  In  the  seventh  generation 
twenty  flowers  on  one  of  these  plants  artificially 
self-fertilised  yielded  no  less  than  nineteen  very  fine 
capsules  ! 

This  variety  transmitted  its  characters  so  faithfully 
to  all  the  succeeding  self-fertilised  generations,  up  to 
the  last  or  ninth,  that  all  the  many  plants  which  were 
raised  presented  a  complete  uniformity  of  character ; 
thus  offering  a  remarkable  contrast  with  the  seedlings 
raised  from  the  purchased  seeds.  Yet  this  variety 
retained  to  the  last  a  latent  tendency  to  produce 
yellow  flowers ;  for  when  a  plant  of  the  eighth  self- 
fertilised  generation  was  crossed  with  pollen  from  a 
yellow-flowered  plant  of  the  Chelsea  stock,  every 
single  seedling  bore  yellow  flowers.  A  similar  variety, 
at  least  in  the  colour  of  its  flowers,  also  appeared 
amongst  the  crossed  plants  of  the  third  generation. 
No  attention  was  at  first  naid  to  it,  and  I  know  not 


80  MIMULTJS  LUTEUS.  Chap.  III. 

how  far  it  was  at  first  used  either  for  crossing  or  self- 
fertilisation.  In  the  fifth  generation  most  of  the 
self-fertilised  plants,  and  in  the  sixth  and  all  the 
succeeding  generations  every  single  plant  consisted  of 
this  variety ;  and  this  no  doubt  was  partly  due  to  its 
great  and  increasing  self-fertility.  On  the  other 
hand,  it  disappeared  from  amongst  the  crossed  plants 
in  the  later  generations;  and  this  was  probably 
due  to  the  continued  intercrossing  of  the  several 
plants.  From  the  tallness  of  this  variety,  the  self- 
fertilised  plants  exceeded  the  crossed  plants  in  height 
in  all  the  generations  from  the  fifth  to  the  seventh 
inclusive;  and  no  doubt  would  have  done  so  in  the 
later  generations,  had  they  been  grown  in  competition 
with  one  another.  In  the  fifth  generation  the  crossed 
plants  were  in  height  to  the  self-fertilised,  as  100  to 
126 ;  in  the  sixth,  as  100  to  147  ;  and  in  the  seventh 
generation,  as  100  to  137.  This  excess  of  height  may 
be  attributed  not  only  to  this  variety  naturally  growing 
taller  than  the  other  plants,  but  to  its  possessing  a 
peculiar  constitution,  so  that  it  did  not  suffer  from 
continued  self-fertilisation. 

This  variety  presents  a  strikingly  analogous  case  to 
that  of  the  plant  called  the  Hero,  which  appeared  in 
the  sixth  self-fertilised  generation  of  Ipomoea.  If 
the  seeds  produced  by  Hero  had  been  as  greatly  in 
excess  of  those  produced  by  the  other  plants,  as  was  the 
case  with  Mimulus,  and  if  all  the  seeds  had  been 
mingled  together,  the  offspring  of  Hero  would  have 
increased  to  the  entire  exclusion  of  the  ordinary 
plants  in  the  later  self-fertilised  generations,  and  from 
naturally  growing  taller  would  have  exceeded  the 
crossed  plants  in  height  in  each  succeeding  generation. 

Some  of  the  self-fertilised  plants  of  the  sixth  gene- 
ration were  intercrossed,  as  were  some  in  the  eighth 


Chap.  III.  DIGITALIS   PURPUREA.  81 

generation ;  and  the  seedlings  from  these  crosses  were 
grown  in  competition  with  self-fertilised  plants  of  the 
two  corresponding  generations.  In  the  first  trial  the 
intercrossed  plants  were  less  fertile  than  the  self- 
fertilised,  and  less  tall  in  the  ratio  of  100  to  110. 
In  the  second  trial,  the  intercrossed  plants  were  more 
fertile  than  the  self-fertilised  in  the  ratio  of  100  to 
73,  and  taller  in  the  ratio  of  100  to  92.  Notwith- 
standing that  the  self-fertilised  plants  in  the  second 
trial  were  the  product  of  two  additional  generations 
of  self-fertilisation,  I  cannot  understand  this  discor- 
dance in  the  results  of  the  two  analogous  experiments. 

The  most  important  of  all  the  experiments  on 
Mimulus  are  those  in  which  flowers  on  plants  of  the 
eighth  self-fertilised  generation  were  again  self-ferti- 
lised ;  other  flowers  on  distinct  plants  of  the  same  lot 
were  intercrossed  ;  and  others  were  crossed  with  a  new 
stock  of  plants  from  Chelsea.  The  Chelsea-crossed 
seedlings  were  to  the  intercrossed  in  height  as  100  to 
56,  and  in  fertility  as  100  to  4 ;  and  they  were  to  the 
self-fertilised  plants,  in  height  as  100  to  52,  and  in 
fertility  as  100  to  3.  These  Chelsea-crossed  plants 
were  also  much  more  hardy  than  the  plants  of  the 
other  two  lots ;  so  that  altogether  the  gain  from  the 
cross  with  a  fresh  stock  was  wonderfully  great. 

Lastly,  seedlings  raised  from  a  cross  between  flowers 
on  the  same  plant  were  not  superior  to  those  from 
flowers  fertilised  with  their  own  pollen ;  but  this  result 
cannot  be  absolutely  trusted,  owing  to  some  previous 
observations,  which,  however,  were  made  under  very 
unfavourable  circumstances. 

Digitalis  purpurea. 

The  flowers  of  the  common  Foxglove  are  proterandrous ;  that 
is,  the  pollen  is  mature  and  mostly  shed  before  the  stigma  of 
the  same  flower  is  ready  for  fertilisation.    This  is  effected  by 


82  DIGITALIS   PUEPUEEA.  Chap.  III. 

the  larger  humble-bees,  which,  whilst  in  search  of  nectar,  carry 
pollen  from  flower  to  flower.  The  two  upper  and  longer 
stamens  shed  their  pollen  before  the  two  lower  and  shorter 
ones.  The  meaning  of  this  fact  probably  is,  as  Dr.  Ogle  re- 
marks,* that  the  anthers  of  the  longer  stamens  stand  near  to 
the  stigma,  so  that  they  would  be  the  most  likely  to  fertilise  it ; 
and  as  it  is  an  advantage  to  avoid  self-fertilisation,  they  shed 
their  pollen  first,  thus  lessening  the  chance.  There  is,  however, 
but  little  danger  of  self-fertilisation  until  the  bifid  stigma 
opens ;  for  Hildebrand  f  found  that  pollen  placed  on  the  stigma 
before  it  had  opened  produced  no  effect.  The  anthers,  which 
are  large,  stand  at  first  transversely  with  respect  to  the  tubular 
corolla,  and  if  they  were  to  dehisce  in  this  position  they  would, 
as  Dr.  Ogle  also  remarks,  smear  with  pollen  the  whole  back  and 
sides  of  an  entering  humble-bee  in  a  useless  manner ;  but  the 
anthers  twist  round  and  place  themselves  longitudinally  before 
they  dehisce.  The  lower  and  inner  side  of  the  mouth  of  the 
corolla  is  thickly  clothed  with  hairs,  and  these  collect  so  much 
of  the  fallen  pollen  that  I  have  seen  the  under  surface  of  a 
humble-bee  thickly  dusted  with  it ;  but  this  can  never  be  ap- 
plied to  the  stigma,  as  the  bees  in  retreating  do  not  turn  their 
under  surfaces  upwards.  I  was  therefore  puzzled  whether  these 
hairs  were  of  any  use ;  but  Mr.  Belt  has,  I  think,  explained 
their  use :  the  smaller  kinds  of  bees  are  not  fitted  to  fertilise 
the  flowers,  and  if  they  were  allowed  to  enter  easily  they  would 
steal  much  nectar,  and  fewer  large  bees  would  haunt  the 
flowers.  Humble-bees  can  crawl  into  the  dependent  flowers 
with  the  greatest  ease,  using  the  "  hairs  as  footholds  while 
sucking  the  honey  ;  but  the  smaller  bees  are  impeded  by 
them,  and  when,  having  at  length  struggled  through  them,  they 
reach  the  slippery  precipice  above,  they  are  completely 
baffled."  Mr.  Belt  says  that  he  watched  many  flowers  during 
a  whole  season  in  North  Wales,  and  "  only  once  saw  a  small 
bee  reach  the  nectary,  though  many  were  seen  trying  in  vain  to 
do  so."  % 

I  covered  a  plant  growing  in  its  native  soil  in  North  Wales 
with  a  net,  and  fertilised  six  flowers  each  with  its  own  pollen, 


*  'Popular    Science    Beview,'  gua,' 1874, p.  132.  But  it  appears 

Jan.  1870,  p.  5G.  from  H.  Miiller  ('  Die  Befruclitung 

t  '  Geschlechter  -  Vertheilung  der  Blumen,'  1873,  p.  285),  that 

bei  den  Pflanzen,'  1867,  p.  20.  small  insects  sometimes   succeed 

X  '  The  Naturalist  in  Nicara-  in  entering  the  flowers. 


Chap.  III.    CKOSSED   AND   SELF-FEKTILISED   PLANTS.        83 

and  six  others  with  pollen  from  a  distinct  plant  growing  within 
the  distance  of  a  few  feet.  The  covered  plant  was  occasionally 
shaken  with  violence,  so  as  to  imitate  the  effects  of  a  gale  of 
wind,  and  thus  to  facilitate  as  far  as  possible  self-fertilisation. 
It  bore  ninety-two  flowers  (besides  the  dozen  artificially  ferti- 
lised), and  of  these  only  twenty-four  produced  capsules ;  whereas 
almost  all  the  flowers  on  the  surrounding  uncovered  plants  were 
fruitful.  Of  the  twenty-four  spontaneously  self-fertilised  cap- 
sules, only  two  contained  their  full  complement  of  seed ;  six 
contained  a  moderate  supply;  and  the  remaining  sixteen  ex- 
tremely few  seeds.  A  little  pollen  adhering  to  the  anthers  after 
they  had  dehisced,  and  accidentally  falling  on  the  stigma  when 
mature,  must  have  been  the  means  by  which  the  above  twenty- 
four  flowers  were  partially  self-fertilised ;  for  the  margins  of  the 
corolla  in  withering  do  not  curl  inwards,  nor  do  the  flowers  in 
dropping  off  turn  round  on  their  axes,  so  as  to  bring  the  pollen- 
covered  hairs,  with  which  the  lower  surface  is  clothed,  into  con- 
tact with  the  stigma — by  either  of  which  means  self- fertilisation 
might  be  effected. 

Seeds  from  the  above  crossed  and  self-fertilised  capsules,  after 
germinating  on  bare  sand,  were  planted  in  pairs  on  the  opposite 
sides  of  five  moderately-sized  pots,  which  were  kept  in  the  green- 
house. The  plants  after  a  time  appeared  starved,  and  were 
therefore,  without  being  disturbed,  turned  out  of  their  pots,  and 
planted  in  the  open  ground  in  two  close  parallel  rows.  They 
were  thus  subjected  to  tolerably  severe  competition  with  one 
another ;  but  not  nearly  so  severe  as  if  they  had  been  left  in  the 
pots.  At  the  time  when  they  were  turned  out,  their  leaves  were 
between  5  and  8  inches  in  length,  and  the  longest  leaf  on 
the  finest  plant  on  each  side  of  each  pot  was  measured,  with  the 
result  that  the  leaves  of  the  crossed  plants  exceeded*  on  an 
average,  those  of  the  self- fertilised  plants  by  •  4  of  an  inch. 

In  the  following  summer  the  tallest  flower-stem  on  each  plant, 
when  fully  grown,  was  measured.  There  were  seventeen  crossed 
plants ;  but  one  did  not  produce  a  flower- stem.  There  were  also, 
originally,  seventeen  self-fertilised  plants,  but  these  had  such 
poor  constitutions  that  no  less  than  nine  died  in  the  course  of 
the  winter  and  spring,  leaving  only  eight  to  be  measured,  as  in 
the  following  table : — 


84 


DIGITALIS   PURPUREA. 


Chap.  III. 


Table  XXIII. 

The  tallest  Flower-stem  on  each  Plant  measured:  0  means  that 

the  Plant  died  before  a  Flower-stem  was  produced. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

Inches. 

Inches 

I. 

53 1 

27  3 

57  a 

55 1 

57 1 

0 

65 

° 

II. 

34| 

39 

52 1 

32 

63  § 

21 

III. 

57  3 

53  3 

53 1 

0 

50  f 

0 

37  § 

0 

IV. 

64 1 

34| 

37  J 

23 1 
0 

V. 

53 

0 

471 

0 

34  f 

0 

Total  in  inches. 

821-25 

287-00 

The  average  height  of  the  flower-stems  of  the  sixteen  crossed 
plants  is  here  51  ■  33  inches ;  and  that  of  the  eight  self-fertilised 
plants,  35"  87 ;  or  as  100  to  70.  But  this  difference  in  height  does 
not  give  at  all  a  fair  idea  of  the  vast  superiority  of  the  crossed 
plants.  These  latter  produced  altogether  sixty-four  flower-stems, 
each  plant  producing,  on  an  average,  exactly  four  flower-stems ; 
whereas  the  eight  self-fertilised  plants  produced  only  fifteen 
flower-stems,  each  producing  an  average  only  of  1  •  87  stems,  and 
these  had  a  less  luxuriant  appearance.  We  may  put  the  result  in 
another  way :  the  number  of  flower-stems  on  the  crossed  plants  was 
to  those  on  an  equal  number  of  self-fertilised  plants  as  100  to  48. 

Three  crossed  seeds  in  a  state  of  germination  were  also  planted 
in  three  separate  pots;  and  three  self-fertilised  seeds  in  the 
same  state  in  three  other  pots.  These  plants  were  therefore 
at  first  exposed  to  no  competition  with  one  another,  and  when 


Chap.  III.   CROSSED   AND   SELF-FERTILISED   PLANTS.        85 

turned  out  of  their  pots  into  the  open  ground  they  were  planted 
at  a  moderate  distance  apart,  so  that  they  were  exposed  to  much 
less  severe  competition  than  in  the  last  case.  The  longest  leaves 
on  the  three  crossed  plants,  when  turned  out,  exceeded  those  on 
the  self-fertilised  plants  by  a  mere  trifle,  viz.,  on  an  average  by 
•17  of  an  inch.  "When  fully  grown  the  three  crossed  plants 
produced  twenty-six  flower-stems ;  the  two  tallest  of  which  on 
each  plant  were  on  an  average  54*04:  inches  in  height.  The 
three  self-fertilised  plants  produced  twenty- three  flower-stems, 
the  two  tallest  of  which  on  each  plant  had  an  average  height  of 
46*18  inches.  So  that  the  difference  between  these  two  lots, 
which  hardly  competed  together,  is  much  less  than  in  the  last 
case  when  there  was  moderately  severe  competition,  namely,  as 
100  to  85,  instead  of  as  100  to  70. 

The  Effects  on  the  Offspring  of  intercrossing  different  Flowers  on 
the  same  Plant,  instead  of  crossing  distinct  Individuals. —  A  fine 
plant  growing  in  my  garden  (one  of  the  foregoing  seedlings)  was 
covered  with  a  net,  and  six  flowers  were  crossed  with  pollen  from 
another  flower  on  the  same  plant,  and  six  others  were  fertilised 
with  their  own  pollen.  All  produced  good  capsules.  The  seeds 
from  each  were  placed  in  separate  watch-glasses,  and  no  difference 
could  be  perceived  by  the  eye  between  the  two  lots  of  seeds ; 
and  when  they  were  weighed  there  was  no  difference  of  any  sig- 
nificance, as  the  seeds  from  the  self-fertilised  capsules  weighed 
7*65  grains,  whilst  those  from  the  crossed  capsules  weighed 
7 '  7  grains.  Therefore  the  sterility  of  the  present  species,  when 
insects  are  excluded,  is  not  due  to  the  impotence  of  pollen 
on  the  stigma  of  the  same  flower.  Both  lots  of  seeds  and  seed- 
lings were  treated  in  exactly  the  same  manner  as  in  the  previous 
table  (XXIII.),  excepting  that  after  the  pairs  of  germinating  seeds 
had  been  planted  on  the  opposite  sides  of  eight  pots,  all  the 
remaining  seeds  were  thickly  sown  on  the  opposite  sides  of  Pots  IX. 
and  X.  in  Table  XXIV.  The  young  plants  during  the  following 
spring  were  turned  out  of  their  pots,  without  being  disturbed, 
and  planted  in  the  open  ground  in  two  rows,  not  very  close 
together,  so  that  they  were  subjected  to  only  moderately  severe 
competition  with  one  another.  Very  differently  to  what  occurred 
in  the  first  experiment,  when  the  plants  were  subjected  to 
somewhat  severe  mutual  competition,  an  equal  number  on  each 
.  side  either  died  or  did  not  produce  flower-stems.  The  tallest 
flower-stems  on  the  surviving  plants  were  measured,  as  shown  in 
the  following  table : 


86 


FLOWERS   ON   SAME   PLANT   CEOSSED.   Chap.  UL 


Table  XXIV. 

N.B.  0  signifies  that  the  Plant  died,  or  did  not  produce  a  Flower- 
stem. 


No.  of  Pot. 

Plants  raised  from  a 
Cross  between  dif- 
ferent Flowers  on  the 
same  Plant. 

Plants  raised  from 

Flowers  fertilised 

with  their  own  Pollen. 

I. 

Inches. 

49 1 
46 1 
43 1 

Inches. 

45 1 

52 

0 

II. 

38 1 

47 1 

0 

54 1 
47 1 
32 1 

III. 

54£ 

46 1 

IV. 

32  k 

0 
431 

41 1 
29  J 
37 1 

V. 

46  § 
40 1 
43 

42 1 

42 1 

0 

VI. 

48§ 
46 1 

47  J 
48 1 

VII. 

48 1 
42 

25 
40§ 

VIII. 

46 1 

39J 

IX. 

Crowded  Plants. 

49 

50g 

46 1 

47 1 

0 

30 1 

15 

36  £ 
44 1 
31§ 

X. 

Crowded  Plants. 

46 1 

35| 

24 1 

•       41| 

17| 

47  J 

0 
345 
40  £ 
418 

Total  inches. 

1078-00 

995-38 

Chap.  III.  CALCEOLAEIA.  87 

The  average  height  of  the  flower-stems  on  the  twenty-five 
crossed  plants  in  all  the  pots  taken  together  is  43 "  12  inches,  and 
that  of  the  twenty-five  self-fertilised  plants  39*82,  or  as  100  to 
92.  In  order  to  test  this  result,  the  plants  planted  in  pairs  in 
Pots  I.  to  VIII.  were  considered  by  themselves,  and  the  average 
height  of  the  sixteen  crossed  plants  is  here  44 "  9,  and  that  of  the 
sixteen  self-fertilised  plants  42*03,  or  as  100  to  94.  Again,  the 
plants  raised  from  the  thickly  sown  seed  in  Pots  IX.  and  X., 
which  were  subjected  to  very  severe  mutual  competition,  were 
taken  by  themselves,  and  the  average  height  of  the  nine  crossed 
plants  is  39  *  86,  and  that  of  the  nine  self-fertilised  plants  35  *  88,  or 
as  100  to  90.  The  plants  in  these  two  latter  pots  (IX.  and  X), 
after  being  measured,  were  cut  down  close  to  the  ground  and 
weighed:  the  nine  crossed  plants  weighed  57*60  ounces,  and 
the  nine  self-fertilised  plants  45*25  ounces,  or  as  100  to  78.  On 
the  whole  we  may  conclude,  especially  from  the  evidence  of 
weight,  that  seedlings  from  a  cross  between  flowers  on  the  same 
plant  have  a  decided,  though  not  great,  advantage  over  those 
from  flowers  fertilised  with  their  own  pollen,  more  especially 
in  the  case  of  the  plants  subjected  to  severe  mutual  competition. 
But  the  advantage  is  much  less  than  that  exhibited  by  the 
crossed  offspring  cf  distinct  plants,  for  these  exceeded  the  self- 
fertilised  plants  in  height  as  100  to  70,  and  in  the  number  of 
flower-stems  as  100  to  48.  Digitalis  thus  differs  from  Ipomcea, 
and  almost  certainly  from  Mimulus,  as  with  these  two  species 
a  cross  between  flowers  on  the  same  plant  did  no  good. 

Calceolaria. 
A  bushy  greenhouse  variety,  with  yellow  flowers  blotched  with  purple. 

The  flowers  in  this  genus  are  constructed  so  as  to  favour  or 
almost  ensure  cross-fertilisation;*  and  Mr.  Anderson  remarks  t 
that  extreme  care  is  necessary  to  exclude  insects  in  order  to 
preserve  any  kind  true.  He  adds  the  interesting  statement,  that 
when  the  corolla  is  cut  quite  away,  insects,  as  far  as  he  has  seen, 
never  discover  or  visit  the  flowers.  This  plant  is,  however,  self- 
fertile  if  insects  are  excluded.  So  few  experiments  were 
made  by  me,  that  they  are  hardly  worth  giving.  Crossed  and 
self-fertilised  seeds  were  sown  on  opposite  sides  of  a  pot,  and 


*   Hildobrand,    as   quoted  by  f  'Gardeners'  Chronicle,'  1853, 

H.     Miiller,    '  Die  Befruchtung       p.  534. 
der  Blumeu,'  1873,  p.  277. 


88  LINAEIA  VULGARIS.  Chap.  III. 

after  a  time  the  crossed  seedlings  slightly  exceeded  the  self- 
fertilised  in  height.  When  a  little  further  grown,  the  longest 
leaves  on  the  former  were  very  nearly  3  inches  in  length, 
whilst  those  on  the  self-fertilised  plants  were  only  2  inches. 
Owing  to  an  accident,  and  to  the  pot  being  too  small,  only  one 
plant  on  each  side  grew  up  and  flowered ;  the  crossed  plant  was 
19j  inches  in  height,  and  the  self-fertilised  one  15  inches;  or  as 
100  to  77. 

LlNARIA  VULGARIS. 

It  has  been  mentioned  in  the  introductory  chapter  that  two 
large  beds  of  this  plant  were  raised  by  me  many  years  ago  from 
crossed  and  self-fertilised  seeds,  and  that  there  was  a  conspicu- 
ous difference  in  height  and  general  appearance  between  the 
two  lots.  The  trial  was  afterwards  repeated  with  more  care ; 
but  as  this  was  one  of  the  first  plants  experimented  on,  my 
usual  method  was  not  followed.  Seeds  were  taken  from  wild 
plants  growing  in  this  neighbourhood  and  sown  in  poor  soil  in 
my  garden.  Five  plants  were  covered  with  a  net,  the  others 
being  left  exposed  to  the  bees,  which  incessantly  visit  the  flowers 
of  this  species,  and  which,  according  to  H.  Midler,  are  the 
exclusive  fertilisers.  This  excellent  observer  remarks  *  that,  as 
the  stigma  lies  between  the  anthers  and  is  mature  at  the  same 
time  with  them,  self-fertilisation  is  possible.  But  so  few  seeds 
are  produced  by  protected  plants,  that  the  pollen  and  stigma  of 
the  same  flower  seem  to  have  little  power  of  mutual  interaction. 
The  exposed  plants  bore  numerous  capsules  forming  solid 
spikes.  Five  of  these  capsules  were  examined  and  appeared  to 
contain  an  equal  number  of  seeds ;  and  these  being  counted  in 
one  capsule,  were  found  to  be  166.  The  five  protected  plants  pro- 
duced altogether  only  twenty-five  capsules,  of  which  five  were 
much  finer  than  all  the  others,  and  these  contained  an  average  of 
23  •  6  seeds,  with  a  maximum  in  one  capsule  of  fifty-five.  So  that 
the  number  of  seeds  in  the  capsules  on  the  exposed  plants  to 
the  average  number  in  the  finest  capsules  on  the  protected 
plants  was  as  100  to  14. 

Some  of  the  spontaneously  self-fertilised  seeds  from  under 
the  net,  and  some  seeds  from  the  uncovered  plants  naturally 
fertilised  and  almost  certainly  intercrossed  by  the  bees,  were 
sown  separately  in  two  large  pots  of  the  same  size ;  so  that  tho 


'  Die  Befruchtang,'  &c.  p.  279. 


Chap.  III.  VEKBASCUM  THAPSUS.  89 

two  lots  of  seedlings  were  not  subjected  to  any  mutual  competi- 
tion. Three  of  the  crossed  plants  when  in  full  flower  were 
measured,  but  no  care  was  taken  to  select  the  tallest  plants; 
their  heights  were  7f,  7f,  and  6|  inches;  averaging  7*08  in 
height.  The  three  tallest  of  all  the  self-fertilised  plants  were 
then  carefully  selected,  and  their  heights  were  6f ,  5f ,  and  5§, 
averaging  5  •  75  in  height.  So  that  the  naturally  crossed  plants 
were  to  the  spontaneously  self-fertilised  plants  in  height,  at 
least  as  much  as  100  to  81. 

VEKBASCUM    THAPSUS. 

The  flowers  of  this  plant  are  frequented  by  various  insects, 
chiefly  by  bees,  for  the  sake  of  the  pollen.  H.  Miiller,  however, 
has  shown  ('  Die  Befruchtung,'  &c.  p.  277)  that  V.  nigrum 
secretes  minute  drops  of  nectar.  The  arrangement  of  the  repro- 
ductive organs,  though  not  at  all  complex,  favours  cross-fer- 
tilisation; and  even  distinct  species  are  often  crossed,  for  a 
greater  number  of  naturally  produced  hybrids  have  been  observed 
in  this  genus  than  in  almost  any  other.*  Nevertheless  the 
present  species  is  perfectly  self-fertile,  if  insects  are  excluded ; 
for  a  plant  protected  by  a  net  was  as  thickly  loaded  with  fine 
capsules  as  the  surrounding  uncovered  plants.  Verbascvm 
lychnitis  is  rather  less  self-fertile,  for  some  protected  plants  did 
not  yield  quite  so  many  capsules  as  the  adjoining  uncovered 
plants. 

Plants  of  V.  thapsvs  had  been  raised  for  a  distinct  purpose 
from  self- fertilised  seeds  ;  and  some  flowers  on  these  plants  were 
again  self-fertilised,  yielding  seed  of  the  second  self-fertilised 
generation ;  and.  other  flowers  were  crossed  with  pollen  from  a 
distinct  plant.  The  seeds  thus  produced  were  sown  on  the 
opposite  sides  of  four  large  pots.  They  germinated,  however,  so 
irregularly  (the  crossed  seedlings  generally  coming  up  first) 
that  I  was  able  to  save  only  six  pairs  of  equal  age.  These  when 
in  full  flower  were  measured,  as  in  the  following  table  (XXV.). 

We  here  see  that  two  of  the  self-fertilised  plants  exceed  in 
height  their  crossed  opponents.  Nevertheless  the  average  height 
of  the  six  crossed  plants  is  65  ■  34  inches,  and  that  of  the  six 
self- fertilised  plants  56 '5  inches;  or  as  100  to  86. 


*  I  have  given  a  striking  case        found  growing  wild :  *  Journal  of 
of  a  large  number  of  such  hybrids        Linn.  Soc.  Bot.'  vol.  x.  p.  451. 
between  V.  thapstis  and  luchnitis 


90 


VANDELLIA  NUMMULAKIFOLIA.  Chap.  Ill, 

Table  XXV. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants 
of  the  Second  Gene- 
ration. 

I. 

Inches. 
76 

Inches. 
53 1 

II. 

54 

66 

III. 

62 
60 1 

75 
30$ 

IV. 

73 
66$ 

62 
52 

Total  in  inches. 

392-13 

339-00 

Vandellia  nummularifolia. 

Seeds  were  sent  to  me  by  Mr.  J.  Scott  from  Calcutta  of  this 
small  Indian  weed,  "which  bears  perfect  and  cleistogene  *  flowers. 
The  latter  are  extremely  small,  imperfectly  developed,  and  never 
expand,  yet  yield  plenty  of  seeds.  The  perfect  and  open 
flowers  are  also  small,  of  a  white  colour  with  purple  marks ;  they 
generally  produce  seed,  although  the  contrary  has  been 
asserted ;  and  they  do  so  even  if  protected  from  insects.  They 
have  a  rather  complicated  structure,  and  appear  to  be  adapted 
for  cross-fertilisation,  but  were  not  carefully  examined  by  me. 
They  are  not  easy  to  fertilise  artificially,  and  it  is  possible  that 
some  of  the  flowers  which  I  thought  that  I  had  succeeded  in 
crossing  were  afterwards  spontaneously  self-fertilised  under  the 
net.  Sixteen  capsules  from  the  crossed  perfect  flowers  contained 
on  an  average  ninety-three  seeds  (with  a  maximum  in  one 
capsule  of  137),  and  thirteen  capsules  from  the  self-fertilised 
perfect  flowers  contained  sixty-two  seeds  (with  a  maximum  in 
one  capsule  of  135) ;  or  as  100  to  67.  But  I  suspect  that  this 
considerable  excess  was  accidental,  as  on  one  occasion  nine 
crossed  capsules  were  compared  with  seven  self-fertilised  cap- 
sules (both  included  in  the  above  number),  and  they  contained 
almost  exactly  the  same  average  number  of  seed.    I  may  add 


*  The  convenient  term  of  cleis- 
togene waa  proposed  by  Kuhn  iu 


an  article  on  the  present  genus  in 
'Bot.  Zeitung,'  1867,  p.  G5. 


Chap,  III.  VANDELLIA  NUM1MIILARTF0LIA.  91 

that  fifteen  capsules  from  self-fertilised  cleistogene  flowers  con- 
tained on  an  average  sixty- four  seeds,  -with  a  maximum  in  one 
of  eighty-seven. 

Crossed  and  self-fertilised  seeds  from  the  perfect  flowers,  and 
other  seeds  from  the  self-fertilised  cleistogene  flowers,  were  sown 
in  five  pots,  each  divided  superficially  into  three  compartments. 
The  seedlings  were  thinned  at  an  early  age,  so  that  twenty 
plants  were  left  in  each  of  the  three  divisions.  The  crossed  plants 
when  in  full  flower  averaged  4  ■  3  inches,  and  the  self-fertilised 
plants  from  the  perfect  flowers  4 "  27  inches  in  height ;  or  as  100 
to  99.  The  self-fertilised  plants  from  the  cleistogene  flowers 
averaged  4-06  inches  in  height;  so  that  the  crossed  were  in 
height  to  these  latter  plants  as  100  to  94. 

I  determined  to  compare  again  the  growth  of  plants  raised 
from  crossed  and  self-fertilised  perfect  flowers,  and  obtained  two 
fresh  lots  of  seeds.  These  were  sown  on  opposite  sides  of  five 
pots,  but  they  were  not  sufficiently  thinned,  so  that  they  grew 
rather  crowded.  When  fully  grown,  all  those  above  2  inches 
in  height  were  selected,  all  below  this  standard  being  rejected ; 
the  former  consisted  of  forty-seven  crossed  and-  forty-one  self- 
fertilised  plants ;  thus  a  greater  number  of  the  crossed  than  of 
the  self-fertilised  plants  grew  to  a  height  of  above  2  inches.  Of 
the  crossed  plants,  the  twenty-four  tallest  were  on  an  average 
3*6  inches  in  height;  whilst  the  twenty-four  tallest  self- 
fertilised  plants  were  3 "  38  inches  in  average  height ;  or  as  100 
to  94.  All  these  plants  were  then  cut  down  close  to  the  ground, 
and  the  forty-seven  crossed  plants  weighed  1090  ■  3  grains,  and 
the  forty- one  self-fertilised  plants  weighed  887' 4  grains.  There- 
fore an  equal  number  of  crossed  and  self-fertilised  would  have 
been  to  each  other  in  weight  as  100  to  97.  From  these  several 
facts  we  may  conclude  that  the  crossed  plants  had  some  real, 
though  very  slight,  advantage  in  height  and  weight  over  the 
self-fertilised  plants,  when  grown  in  competition  with  one 
another. 

The  crossed  plants  were,  however,  inferior  in  fertility  to  the 
self-fertilised.  Six  of  the  finest  plants  were  selected  out  of  the 
forty-seven  crossed  plants,  and  six  out  of  the  forty-one  self- 
fertilised  plants ;  and  the  former  produced  598  capsules,  whilst 
the  latter  or  self-fertilised  plants  produced  752  capsules.  All 
these  capsules  were  the  product  of  cleistogene  flowers,  for  the 
plants  did  not  bear  during  the  whole  of  this  season  any  perfect 
flowers.    The  seeds  were  counted  in  ten  cleistogene  capsules 


92 


GESNEKIA   PENDULINA. 


Chap.  III. 


produced  by  the  crossed  plants,  and  their  average  number  was 
46*4  per  capsule;  whilst  the  number  in  ten  cleistogene  capsules 
produced  by  the  self-fertilised  plants  was  49  "4 ;  or  as  100  to  106. 

III.  GESNEPJACE^.— Gesneria  pendtjlina. 

In  Gesneria  the  several  parts  of  the  flower  are  arranged  on 
nearly  the  same  plan  as  in  Digitalis,*  and  most  or  all  of  the 
species  are  dichogamous.  Plants  were  raised  from  seed  sent  me 
by  Fritz  Miiller  from  South  Brazil.  Seven  flowers  were  crossed 
with  pollen  from  a  distinct  plant,  and  produced  seven  capsules 
containing  by  weight  3-01  grains  of  seeds.  Seven  flowers  on  the 
same  plants  were  fertilised  with  their  own  pollen,  and  their 
seven  capsules  contained  exactly  the  same  weight  of  seeds. 
Germinating  seeds  were  planted  on  opposite  sides  of  four  pots, 
and  when  fully  grown  measured  to  the  tips  of  their  leaves. 

Table  XXVI. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
42 1 
24  J 

Inches. 
39 
271 

II. 

33 
27 

30| 
19] 

III. 

33 1 

29  j 

31? 
28  § 

IV. 

30 1 
36 

29 1 
26 1 

Total  inches. 

256-50 

233-13 

The  average  height  of  the  eight  crossed  plants  is  32-06  inches, 
and  that  of  the  eight  self-fertilised  plants  29-14;  or  as  100 
to  90. 


*  Dr.  Ogle, '  Popular  Science  Eeview,'  Jan.  1870,  p.  51. 


Chap.  III. 


SALVIA   COCCINEA. 


93 


IV.  LABIATE.— Salvia  coccinea.* 

This  species,  unlike  most  of  the  others  in  the  same  genus, 
yields  a  good  many  seeds  when  insects  are  excluded.  I  gathered 
ninety-eight  capsules  produced  by  flowers  spontaneously  self- 
fertilised  under  a  net,  and  they  contained  on  an  average  1*45 
seeds,  whilst  flowers  artificially  fertilised  with  their  own  pollen, 
in  which  case  the  stigma  will  have  received  plenty  of  pollen, 
yielded  on  an  average  3'3  seeds,  or  more  than  twice  as  many. 
Twenty  flowers  were  crossed  with  pollen  from  a  distinct  plant, 
and  twenty-six  were  self-fertilised.  There  was  no  great  difference 
in  the  proportional  number  of  flowers  which  produced  capsules 
by  these  two  processes,  or  in  the  number  of  the  contained  seeds, 
or  in  the  weight  of  an  equal  number  of  seeds. 

Seeds  of  both  kinds  were  sown  rather  thickly  on  opposite  sides 
of  three  pots.  When  the  seedlings  were  about  3  inches  in 
height,  the  crossed  showed  a  slight  advantage  over  the  self- 
fertilised.  When  two-thirds  grown,  the  two  tallest  plants  on 
each  side  of  each  pot  were  measured ;  the  crossed  averaged  16 "  37 
inches,  and  the  self-fertilised  11*75  in  height;  or  as  100  to  71. 
When  the  plants  were  fully  grown  and  had  done  flowering,  the 
two  tallest  plants  on  each  side  were  again  measured,  with  the 
results  shown  in  the  following  table : — 


Table  XXYII. 


No.  of  Pot. 

Crossed  Plants. 

Self- fertilised  Plants. 

I. 

Inches. 
32 1 
20 

Inches. 
25 
18f 

II. 

32| 

24| 

20  § 
19| 

III. 

29 1 
28 

25 
18 

Total  inches. 

167-13 

127-00 

*  The  admirable  mechanical 
adaptations  in  this  genus  for 
favouring  or  ensuring  cross-ferti- 
lisation, have  been  fully  described 


by  Sprengel,  Hildebrand,  Delpino, 
H.  Midler,  Ogle,  and  others,  in 
their  several  works. 


94  OBIGANUM  VULGAKE.  Chap.  III. 

It  may  be  here  seen  that  each  of  the  six  tallest  crossed  plants 
exceeds  in  height  its  self-fertilised  opponent;  the  former 
averaged  27 '85  inches,  whilst  the  six  tallest  self-fertilised  plants 
averaged  21  ■  16  inches ;  or  as  100  to  76.  In  all  three  pots  the 
first  plant  which  flowered  was  a  crossed  one.  All  the  crossed 
plants  together  produced  409  flowers,  whilst  all  the  self-fertilised 
together  produced  only  232  flowers ;  or  as  100  to  57.  So  that 
the  crossed  plants  in  this  respect  were  far  more  productive  than 
the  self-fertilised. 

Origanum  vulgare. 

This  plant  exists,  according  to  H.  Muller,  under  two  forms ; 
one  hermaphrodite  and  strongly  proterandrous,  so  that  it  is 
almost  certain  to  be  fertilised  by  pollen  from  another  flower ; 
the  other  form  is  exclusively  female,  has  a  smaller  corolla,  and 
must  of  course  be  fertilised  by  pollen  from  a  distinct  plant 
in  order  to  yield  any  seeds.  The  plants  on  which  I  experi- 
mented were  hermaphrodites ;  they  had  been  cultivated  for  a 
long  period  as  a  pot-herb  in  my  kitchen  garden,  and  were,  like 
so  many  long-cultivated  plants,  extremely  sterile.  As  I  felt 
doubtful  about  the  specific  name  I  sent  specimens  to  Kew,  and 
was  assured  that  the  species  was  O.  vulgare.  My  plants  formed 
one  great  clump,  and  had  evidently  spread  from  a  single  root 
by  stolons.  In  a  strict  sense,  therefore,  they  all  belonged  to  the 
same  individual.  My  object  in  experimenting  on  them  was, 
firstly,  to  ascertain  whether  crossing  flowers  borne  by  plants 
having  distinct  roots,  but  all  derived  asexually  from  the  same 
individual,  would  be  in  any  respect  more  advantageous  than 
self-fertilisation ;  and,  secondly,  to  raise  for  future  trial  seedlings 
which  would  constitute  really  distinct  individuals.  Several 
plants  in  the  above  clump  were  covered  by  a  net,  and  about  two 
dozen  seeds  (many  of  which,  however,  were  small  and  withered) 
were  obtained  from  the  flowers  thus  spontaneously  self-fertilised. 
The  remainder  of  the  plants  were  left  uncovered  and  were  in- 
cessantly visited  by  bees,  so  that  they  were  doubtless  crossed 
by  them.  These  exposed  plants  yielded  rather  more  and  finer 
seed  (but  still  very  few)  than  did  the  covered  plants.  The  two 
lots  of  seeds  thus  obtained  were  sown  on  opposite  sides  of  two 
pots ;  the  seedlings  were  carefully  observed  from  their  first 
growth  to  maturity,  but  they  did  not  differ  at  any  period  in 
height  or  in  vigour,  the  importance  of  which  latter  observation 
we  shall  presently  see.    When  fully  grown,  the  tallest  crossed 


Chap.  III. 


OEIGANUM  VULGARE. 


95 


plant  in  one  pot  was  a  very  little  taller  than  the  tallest  self- 
fertilised  plant  on  the  opposite  side,  and  in  the  other  pot 
exactly  the  reverse  occurred.  So  that  the  two  lots  were  in  fact 
equal ;  and  a  cross  of  this  kind  did  no  more  good  than  crossing 
two  flowers  on  the  same  plant  of  Ipomcea  or  Mimulus. 

The  plants  were  turned  out  of  the  two  pots  without  being 
disturbed  and  planted  in  the  open  ground,  in  order  that  they 
might  grow  more  vigorously.  In  the  following  summer  all  the 
self-fertilised  and  some  of  the  quasi-crossed  plants  were  covered 
by  a  net.  Many  flowers  on  the  latter  were  crossed  by  me  with 
pollen  from  a  distinct  plant,  and  others  were  left  to  be  crossed 
by  the  bees.  These  quasi-crossed  plants  produced  rather  more 
seed  than  did  the  original  ones  in  the  great  clump  when  left 
to  the  action  of  the  bees.  Many  flowers  on  the  self-fertilised 
plants  were  artificially  self-fertilised,  and  others  were  allowed 
to  fertilise  themselves  spontaneously  under  the  net,  but  they 
yielded  altogether  very  few  seeds.  These  two  lots  of  seeds — 
the  product  of  a  cross  between  distinct  seedlings,  instead  of  as 
in  the  last  case  between  plants  multiplied  by  stolons,  and  the 
product  of  self-fertilised  flowers — were  allowed  to  germinate  on 
bare  sand,  and  several  equal  pairs  were  planted  on  opposite 
sides  of  two  large  pots.  At  a  very  early  age  the  crossed 
plants  showed  some  superiority  over  the  self-fertilised,  which 
was  ever  afterwards  retained.  When  the  plants  were  fully 
grown,  the  two  tallest  crossed  and  the  two  tallest  self-fertilised 
plants  in  each  pot  were  measured,  as  shown  in  the  following 
table.  I  regret  that  from  want  of  time  I  did  not  measure  all 
the  pairs ;  but  the  tallest  on  each  side  seemed  fairly  to  represent 
the  average  difference  between  the  two  lots. 

Table  XXVIII. 


No.  of  Pot. 

Crossed  Plants  (two 
tallest  in  each  pot). 

Srlf-fertilised  Plants 

(two  tallest  in  each 

pot). 

I. 

Inches. 
26 
21 

Inches. 

24 
21 

II. 

17 
16 

12 
HI 

Total  inches. 

80-0 

68-5 

96  THUNBERGIA  ALATA.        Chap.  III. 

The  average  height  of  the  crossed  plants  is  here  20  inches,  and 
that  of  the  self-fertilised  17-12 ;  or  as  100  to  86.  But  this  excess 
of  height  by  no  means  gives  a  fair  idea  of  the  vast  superiority  in 
vigour  of  the  crossed  over  the  self-fertilised  plants.  The  crossed 
flowered  first  and  produced  thirty  flower-stems,  whilst  the  self- 
fertilised  produced  only  fifteen,  or  half  the  number.  The  pots 
were  then  bedded  out,  and  the  roots  probably  came  out  of  the 
holes  at  the  bottom  and  thus  aided  their  growth.  Early  in  the 
following  summer  the  superiority  of  the  crossed  plants,  owing 
to  their  increase  by  stolons,  over  the  self-fertilised  plants  was 
truly  wonderful.  In  Pot  I.,  and  it  should  be  remembered  that 
very  large  pots  had  been  used,  the  oval  clump  of  crossed  plants 
was  10  by  4|  inches  across,  with  the  tallest  stem,  as  yet  young, 
5£  inches  in  height ;  whilst  the  clump  of  self-fertilised  plants, 
on  the  opposite  side  of  the  same  pot,  was  only  3i  by  2|  inches 
across,  with  the  tallest  young  stem  4  inches  in  height.  In  Pot 
II.,  the  clump  of  crossed  plants  was  18  by  9  inches  across,  with 
the  tallest  young  stem  8s  inches  in  height;  whilst  the  clump  of 
self-fertilised  plants  on  the  opposite  side  of  the  same  pot  was  12 
by  4s  inches  across,  with  the  tallest  young  stem  6  inches  in 
height.  The  crossed  plants  during  this  season,  as  during  the 
last,  flowered  first.  Both  the  crossed  and  self-fertilised  plants 
being  left  freely  exposed  to  the  visils  of  bees,  manifestly  produced 
much  more  seed  than  their  grand-parents, — the  plants  of  the 
original  clump  still  growing  close  by  in  the  same  garden,  and 
equally  left  to  the  action  of  the  bees. 

V.  ACANTETACEiE—  Thustbebgia  alata. 

It  appears  from  Hildebrand's  description  Q  Bot.  Zeitung,'  1867, 
p.  285)  that  the  conspicuous  flowers  of  this  plant  are  adapted 
for  cross-fertilisation.  Seedlings  were  twice  raised  from  pur- 
chased seed ;  but  during  the  early  summer,  when  first  expe- 
rimented on,  they  were  extremely  sterile,  many  of  the  anthers 
containing  hardly  any  pollen.  Nevertheless,  during  the  autumn 
these  same  plants  spontaneously  produced  a  good  many  seeds. 
Twenty-six  flowers  during  the  two  years  were  crossed  with 
pollen  from  a  distinct  plant,  but  they  yielded  only  eleven 
capsules;  and  these  contained  very  few  seeds!  Twenty-eight 
flowers  were  fertilised  with  pollen  from  the  same  flower,  and 
these  yielded  only  ten  capsules,  which,  however,  contained 
rather  more  seed  than  the  crossed  capsules.    Eight  pairs  of 


Chap.  UI.  THUNBEEGIA  ALATA.  97 

germinating  seeds  were  planted  on  opposite  sides  of  five  pots; 
and  exactly  half  the  crossed  and  half  the  self-fertilised  plants 
exceeded  their  opponents  in  height.  Two  of  the  self-fertilised 
plants  died  young,  before  they  were  measured,  and  their  crossed 
opponents  were  thrown  away.  The  six  remaining  pairs  grew 
very  unequally,  some,  both  of  the  crossed  and  self-fertilised 
plants,  being  more  than  twice  as  tall  as  the  others.  The  average 
height  of  the  crossed  plants  was  60  inches,  and  that  of  the  self- 
fertilised  plants  65  inches,  or  as  100  to  108.  A  cross,  therefore, 
between  distinct  individuals  here  appears  to  do  no  good ;  but 
this  result  deduced  from  so  few  plants  in  a  very  sterile  condition 
and  growing  very  unequally,  obviously  cannot  be  trusted. 


98  BEASSICA  OLEEACEA.  Chai\  IV. 


CHAPTER  IV. 

Crcoieer^,  Papavekace.e,  Eesedace.®,  etc. 

Brassica  oleracea,  crossed  and  self-fertilised  plants — Great  effect  of  a 
cross  with  a  fresh  stock  on  the  weight  of  the  offspring — Iberis 
umbellata — Papaver  vagum — Eschscholtzia  califomica,  seedlings 
from  a  cross  with  a  fresh  stock  not  more  vigorous,  but  more 
fertile  than  the  self-fertilised  seedlings — Eesedalutea  and  odorata, 
many  individuals  sterile  with  their  own  pollen — Viola  tricolor, 
wonderful  effects  of  a  cross — Adonis  aestivalis — Delphinium  consolida 
— Viscaria  oculata,  crossed  plants  hardly  taller,  but  more  fertile  than 
the  self-fertilised — Dianthus  caryophyllus,  crossed  and  self-fertilised 
plants  compared  for  four  generations — Great  effects  of  a  cross  with 
a  fresh  stock — Uniform  colour  of  the  flowers  on  the  self-fertilised 
plants — Hibiscus  africanus. 

VI.  CEUCIFEBJE.— Bbassica  oleeacea. 
Var.  Cattell's  Early  Barnes  Cabbage. 

The  flowers  of  the  common  cabbage  are  adapted,  as  shown  by 
H.  Miiller,*  for  cross-fertilisation,  and  should  this  fail,  for  self- 
fertilisation.  It  is  well  known  that  the  varieties  are  crossed  so 
largely  by  insects,  that  it  is  impossible  to  raise  pure  kinds  in  the 
same  garden,  if  more  than  one  kind  is  in  flower  at  the  same  time. 
Cabbages,  in  one  respect,  were  not  well  fitted  for  my  experiments, 
as,  after  they  had  formed  heads,  they  were  often  difficult  to  mea- 
sure. The  flower-stems  also  differ  much  in  height ;  and  a  poor 
plant  will  sometimes  throw  up  a  higher  stem  than  that  of  a  fine 
plant.  In  the  later  experiments,  the  fully-grown  plants  were  cut 
down  and  weighed,  and  then  the  immense  advantage  from  a 
cross  became  manifest. 

A  single  plant  of  the  above  variety  was  covered  with  a  net 
just  before  flowering,  and  was  crossed  with  pollen  from  another 
plant  of  the  same  variety  growing  close  by ;  and  the  seven  cap- 
su^s  thus  produced  contained  on  an  average  16 '3  seeds,  with  a 


'Die  Befruchtung,'  &c.  p.  139. 


Chap.  IV.    CROSSED   AND   SELF-FERTILISED   PLANTS.        99 

maximum  of  twenty  in  one  capsule.  Some  flowers  were  arti- 
ficially self-fertilised,  but  their  capsules  did  not  contain  so  many 
seeds  as  those  from  flowers  spontaneously  self- fertilised  under 
the  net,  of  which  a  considerable  number  were  produced.  Fourteen 
of  these  latter  capsules  contained  on  an  average  4"1  seeds,  with 
a  maximum  in  one  of  ten  seeds ;  so  that  the  seeds  in  the  crossed 
capsules  were  in  number  to  those  in  the  self-fertilised  capsules  as 
100  to  25.  The  self-fertilised  seeds,  fifty-eight  of  which  weighed 
3 "  88  grains,  were,  however,  a  little  finer  than  those  from  the 
crossed  capsules,  fifty-eight  of  which  weighed  3 "  76  grains.  When 
few  seeds  are  produced,  these  seem  often  to  be  better  nourished 
and  to  be  heavier  than  when  many  are  produced. 

The  two  lots  of  seeds  in  an  equal  state  of  germination  were 
planted,  some  on  opposite  sides  of  a  single  pot,  and  some  in  the 
open  ground.  The  young  crossed  plants  in  the  pot  at  first  ex- 
ceeded by  a  little  in  height  the  self-fertilised ;  then  equalled  them ; 
were  then  beaten;  and  lastly  were  again  victorious.  The  plants, 
without  being  disturbed,  were  turned  out  of  the  pot,  and  planted 
in  the  open  ground;  and  after  growing  for  some  time,  the 
crossed  plants,  which  were  all  of  nearly  the  same  height,  exceeded 
the  self-fertilised  ones  by  2  inches.  When  they  flowered,  the 
flower-stems  of  the  tallest  crossed  plant  exceeded  that  of  the 
tallest  self-fertilised  plant  by  6  inches.  The  other  seedlings 
which  were  planted  in  the  open  ground  stood  separate,  so  that 
they  did  not  compete  with  one  another ;  nevertheless  the  crossed 
plants  certainly  grew  to  a  rather  greater  height  than  the  self-fer- 
tilised ;  but  no  measurements  were  made.  The  crossed  plants 
which  had  been  raised  in  the  pot,  and  those  planted  in  the  open 
ground,  all  flowered  a  little  before  the  self-fertilised  plants. 

Crossed  and  selj "-fertilised  Plants  of  the  Second  Generation. — Some 
flowers  on  the  crossed  plants  of  the  last  generation  were  again 
crossed  with  pollen  from  another  crossed  plant,  and  produced 
fine  capsules.  The  flowers  on  the  self-fertilised  plants  of  the 
last  generation  were  allowed  to  fertilise  themselves  spontaneously 
under  a  net,  and  they  produced  some  remarkably  fine  capsules. 
The  two  lots  of  seeds  thus  produced  germinated  on  sand,  and 
eight  pairs  were  planted  on  opposite  sides  of  four  pots.  These 
plants  were  measured  to  the  tips  of  their  leaves  on  the 
20th  of  October  of  the  same  year,  and  the  eight  crossed  plants 
averaged  in  height  8*4  inches,  whilst  the  self-fertilised  averaged 
8  •  53  inches,  so  that  the  crossed  were  a  little  inferior  in  height, 
as  100  to  101  •  5.     By  the  5th  of  June  of  the  following  year  these 


100 


BEASSICA  OLEEACEA. 


Chap.  IV 


plants  had  grown  much  bulkier,  and  had  begun  to  form 
heads.  The  crossed  had  now  acquired  a  marked  superiority 
in  general  appearance,  and  averaged  8-02  inches  in  height, 
whilst  the  self-fertilised  averaged  7 '  31  inches ;  or  as  100  to  91. 
The  plants  were  then  turned  out  of  their  pots  and  planted 
undisturbed  in  the  open  ground.  By  the  5th  of  August  their 
heads  were  fully  formed,  but  several  had  grown  so  crooked  that 
their  heights  could  hardly  be  measured  with  accuracy.  The 
crossed  plants,  however,  were  on  the  whole  considerably  taller 
than  the  self-fertilised.  In  the  following  year  they  flowered ;  the 
crossed  plants  flowering  before  the  self-fertilised  in  three  of  the 
pots,  and  at  the  same  time  in  Pot  II.  The  flower-stems  were 
now  measured,  as  shown  in  Table  XXIX. 

Table  XXIX. 

Measured  to  tops  of  Flower-stems ;  0  signifies  that  a  Flower-stem 

was  not  formed. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
49  § 
39 1 

Inches. 
44 
41 

II. 

37 1 
33 1 

38 
35  $ 

in. 

47 
40 
42 

51  i 
41 1 
46 1 

IV. 

43 1 

37  § 

0 

20§ 

33 1 

0 

Total  in  inches. 

369-75 

351-00 

The  nine  flower-stems  on  the  crossed  plants  here  average  41*  08 
inches,  and  the  nine  on  the  self-fertilised  plants  39  inches  in 
height,  or  as  100  to  95.  But  this  small  difference,  which,  more- 
over, depended  almost  wholly  on  one  of  the  self-fertilised  plants 
being  only  20  inches  high,  does  not  in  the  least  show  the  vast 
superiority  of  the  crossed  over  the  self-fertilised  plants.  Both 
lots,  including  the  two  plants  in  Pot  IV.,  which  did  not 
flower,  were  now  cut  down  close  to  the  ground  and  weighed,  but 


Chap.  IV. 


CEOSS   WITH  A   FEESH  STOCK. 


101 


those  in  Pot  II.  were  excluded,  for  they  had  been  accidentally 
injured  by  a  fall  during  transplantation,  and  one  was  almost 
killed.  The  eight  crossed  plants  weighed  219  ounces,  whilst  the 
eight  self-fertilised  plants  weighed  only  82  ounces,  or  as  100  to  37 ; 
so  that  the  superiority  of  the  former  over  the  latter  in  weight  was 
great. 

The  Effects  of  a  Cross  with  a  fresh  Stock. — Some  flowers  on  a 
crossed  plant  of  the  last  or  second  generation  were  fertilised, 
without  being  castrated,  by  pollen  taken  from  a  plant  of  the 
same  variety,  but  not  related  to  my  plants,  and  brought  from  a 
nursery  garden  (whence  my  seeds  originally  came)  having  a  dif- 
ferent soil  and  aspect.  The  flowers  on  the  self-fertilised  plants 
of  the  last  or  second  generation  (Table  XXIX.)  were  allowed  to 
fertilise  themselves  spontaneously  under  a  net,  and  yielded 
plenty  of  seeds.  These  latter  and  the  crossed  seeds,  after  germi- 
nating on  sand,  were  planted  in  pairs  on  the  opposite  sides 
of  six  large  pots,  which  were  kept  at  first  in  a  cool  greenhouse. 
Early  in  January  their  heights  were  measured  to  the  tips  of  their 
leaves.  The  thirteen  crossed  plants  averaged  13  "16  inches  in 
height,  and  the  twelve  (for  one  had  died)  self-fertilised  plants 
averaged  13  ■  7  inches,  or  as  100  to  104 ;  so  that  the  self-fertilised 
plants  exceeded  by  a  little  the  crossed  plants. 


Table  XXX. 

Weight  of  Plants  after  they  had  formed  Heads. 


No.  of  Pot. 

Crossed  Plants  from 
Pollen  of  fresh  Stock. 

Self-fertiltsed  Plants 
of  the  Third  Gene- 
ration. 

I. 

Ounces. 
130 

Ounces. 
18| 

II. 

74 

34 1 

III. 

121 

17| 

IV. 

127| 

14 

V. 

90 

11| 

VI. 

106 1 

46 

Total  in  ounces. 

649-00 

142*25 

102  BEASSICA  OLERACEA.  Chap.  IV. 

Early  in  the  spring  the  plants  were  gradually  hardened,  and 
turned  out  of  their  pots  into  the  open  ground  without  being 
disturbed.  By  the  end  of  August  the  greater  number  had 
formed  fine  heads,  but  several  grew  extremely  crooked,  from 
having  been  drawn  up  to  the  light  whilst  in  the  greenhouse. 
As  it  was  scarcely  possible  to  measure  their  heights,  the  finest 
plant  on  each  side  of  each  pot  was  cut  down  close  to  the  ground 
and  weighed.     In  the  preceding  table  we  have  the  result. 

The  six  finest  crossed  plants  average  108*16  ounces,  whilst 
the  six  finest  self-fertilised  plants  average  only  23 "  7  ounces,  or 
as  100  to  22.  This  difference  shows  in  the  clearest  manner  the 
enormous  benefit  which  these  plants  derived  from  a  cross  with 
another  plant  belonging  to  the  same  sub-variety,  but  to  a  fresh 
stock,  and  grown  during  at  least  the  three  previous  generations 
under  somewhat  different  conditions. 

The  Offspring  from  a  cut-leaved,  curled,  and  variegated  white- 
green  Cabbage  crossed  with  a  cut-leaved,  curled,  and  variegated 
crimson-green  Cabbage,  compared  with  the  self-fertilised  Offspring 
from  the  two  Varieties. — These  trials  were  made,  not  for  the 
sake  of  comparing  the  growth  of  the  crossed  and  self-fertilised 
seedlings,  but  because  I  had  seen  it  stated  that  these  varieties 
would  not  naturally  intercross  when  growing  uncovered  and 
near  one  another.  This  statement  proved  quite  erroneous ;  but 
the  white-green  variety  was  in  some  degree  sterile  in  my  garden, 
producing  little  pollen  and  few  seeds.  It  was  therefore  no 
wonder  that  seedlings  raised  from  the  self-fertilised  flowers  of  this 
variety  were  greatly  exceeded  in  height  by  seedlings  from  a  cross 
between  it  and  the  more  vigorous  crimson-green  variety;  and 
nothing  more  need  be  said  about  this  experiment. 

The  seedlings  from  the  reciprocal  cross,  that  is,  from  the  crim- 
son-green variety  fertilised  with  pollen  from  the  white-green 
variety,  offer  a  somewhat  more  curious  case.  A  few  of  these 
crossed  seedlings  reverted  to  a  pure  green  variety  with  their 
leaves  less  cut  and  curled,  so  that  they  were  altogether  in  a  much 
more  natural  state,  and  these  plants  grew  more  vigorously  and 
taller  than  any  of  the  others.  Now  it  is  a  strange  fact  that  a 
much  larger  number  of  the  self-fertilised  seedlings  from  the 
crimson-green  variety  than  of  the  crossed  seedlings  thus  reverted ; 
and  as  a  consequence  the  self-fertilised  seedlings  grew  taller  by 
2i  inches  on  an  average  than  the  crossed  seedlings,  with  which 
they  were  put  into  competition.  At  first,  however,  the  crossed 
seedlings  exceeded  the  self-fertilised  by  an  average  of  a  quarter 


Cuap.  IV.  IBEEIS  UMBELLATA.  103 

of  an  inch.  We  thus  see  that  reversion  to  a  more  natural  con- 
dition acted  more  powerfully  in  favouring  the  ultimate  growth 
of  these  plants  than  did  a  cross ;  but  it  should  be  remembered 
that  the  cross  was  with  a  semi-sterile  variety  having  a  feeble 
constitution. 

IBESIS   UMBELLATA. 
Var.  Kermesiana. 

This  variety  produced  plenty  of  spontaneously  self-fertilised 
seed  under  a  net.  Other  plants  in  pots  in  the  greenhouse  were 
left  uncovered,  and  as  I  saw  small  flies  visiting  the  flowers,  it 
seemed  probable  that  they  would  be  intercrossed.  Consequently 
seeds  supposed  to  have  been  thus  crossed  and  spontaneously  self- 
fertilised  seeds  were  sown  on  opposite  sides  of  a  pot.  The 
self-fertilised  seedlings  grew  from  the  first  quicker  than  the 
supposed  crossed  seedlings,  and  when  both  lots  were  in  full 
flower  the  former  were  from  5  to  6  inches  higher  than  the  crossed ! 
I  record  in  my  notes  that  the  self-fertilised  seeds  from  which 
these  self-fertilised  plants  were  raised  were  not  so  well  ripened 
as  the  crossed ;  and  this  may  possibly  have  caused  the  great 
difference  in  their  growth,  in  a  somewhat  analogous  manner 
as  occurred  with  the  self-fertilised  plants  of  the  eighth  generation 
of  Ipomoea  raised  from  unhealthy  parents.  It  is  a  curious 
circumstance,  that  two  other  lots  of  the  above  seeds  were 
sown  in  pure  sand  mixed  with  burnt  earth,  and  therefore  with- 
out any  organic  matter;  and  here  the  supposed  crossed 
seedlings  grew  to  double  the  height  of  the  self-fertilised,  before 
both  lots  died,  as  necessarily  occurred  at  an  early  period.  We 
shall  hereafter  meet  with  another  case  apparently  analogous 
to  this  of  Iberis  in  the  third  generation  of  Petunia. 

The  above  self-fertilised  plants  were  allowed  to  fertilise  them- 
selves again  under  a  net,  yielding  self-fertilised  plants  of  the 
second  generation,  and  the  supposed  crossed  plants  were  crossed 
by  pollen  of  a  distinct  plant ;  but  from  want  of  time  this  was  dono 
in  a  careless  manner,  namely,  by  smearing  one  head  of  expanded 
flowers  over  another.  I  should  have  thought  that  this  would 
have  succeeded,  and  perhaps  it  did  so;  but  the  fact  of  108 
of  the  self-fertilised  seeds  weighing  4*87  grains,  whilst  the  same 
number  of  the  supposed  crossed  seeds  weighed  only  3 "  57  grains, 
does  not  look  like  it.  Five  seedlings  from  each  lot  of  seeds  were 
raised,  and  the  self-fertilised  plants,  when  fully  grown,  exceeded 


104 


IBERIS   UMBELLATA. 


Chap.  IV. 


in  average  height  by  a  trifle  (viz.  "4  of  an  inch)  the  five  probably 
crossed  plants.  I  have  thought  it  right  to  give  this  case  and  the 
last,  because  had  the  supposed  crossed  plants  proved  superior 
to  the  self-fertilised  in  height,  I  should  have  assumed  without 
doubt  that  the  former  had  really  been  crossed.  As  it  is,  I  do  not 
know  what  to  conclude. 

Being  much  surprised  at  the  two  foregoing  trials,  I  deter- 
mined to  make  another,  in  which  there  should  be  no  doubt  about 
the  crossing.  I  therefore  fertilised  with  great  care  (but  as 
usual  without  castration)  twenty-four  flowers  on  the  supposed 
crossed  plants  of  the  last  generation  with  pollen  from  distinct 
plants,  and  thus  obtained  twenty-one  capsules.  The  self-fertilised 
plants  of  the  last  generation  were  allowed  to  fertilise  themselves 
again  under  a  net,  and  the  seedlings  reared  from  these  seeds 
formed  the  third  self-fertilised  generation.  Both  lots  of  seeds, 
after  germinating  on  bare  sand,  were  planted  in  pairs  on 
the  opposite  sides  of  two  pots.  All  the  remaining  seeds  were 
sown  crowded  on  opposite  sides  of  a  third  pot ;  but  as  all  the 
self-fertilised  seedlings  in  this  latter  pot  died  before  they  grew 
to  any  considerable  height,  they  were  not  measured.  The 
plants  in  Pots  I.  and  II.  were  measured  when  between  7  and 
8  inches  in  height,  and  the  crossed  exceeded  the  self- fertilised 
in  average  height  by  1  •  57  inches.  "When  fully  grown  they  were 
again  measured  to  the  summits  of  their  flower-heads,  with  the 
following  result : — 

Table  XXXI. 


No.  of  Pot. 

r™=wpd  Plants       '  Solf-fertilised  Plants 
Crossed  Plants.          of  the  Third  Gene- 
ration. 

I. 

Inches. 
18 
21 
18§ 

Inches. 
19 
21 
19 1 

II. 

19 
18f 
.    17f 
21  § 

16 1 

n 

14| 
16| 

Total  in  inches. 

133-88 

114-75 

The  average  height  of  the  seven  crossed    lants  is  here  19 '  12 


Chai\  IV.  CROSS  WITH  A   FRESH   STOCK.  105 

inches,  and  that  of  the  seven  self-fertilised  plants  16*39,  or  as 
100  to  86.  But  as  the  plants  on  the  self-fertilised  side  grew 
very  unequally,  this  ratio  cannot  be  fully  trusted,  and  is  probably 
too  high.  In  both  pots  a  crossed  plant  flowered  before  any  one 
of  the  self-fertilised.  These  plants  "were  left  uncovered  in  the 
greenhouse ;  but  from  being  too  much  crowded  they  were  not 
very  productive.  The  seeds  from  all  seven  plants  of  both  lots 
were  counted ;  the  crossed  produced  206,  and  the  self-fertilised 
154;  or  as  100  to  75. 

Cross  by  a  fresh  Stock. — From  the  doubts  caused  by  the  two 
first  trials,  in  which  it  was  not  known  with  certainty  that  the 
plants  had  been  crossed;  and  from  the  crossed  plants  in  the 
last  experiment  having  been  put  into  competition  with  plants 
self-fertilised  for  three  generations,  which  moreover  grew  very 
unequally,  I  resolved  to  repeat  the  trial  on  a  larger  scale,  and 
in  a  rather  different  manner.  I  obtained  seeds  of  the  same 
crimson  variety  of  J.  umbellata  from  another  nursery  garden, 
and  raised  plants  from  them.  Some  of  these  plants  were  allowed 
to  fertilise  themselves  spontaneously  under  a  net ;  others  were 
crossed  by  pollen  taken  trum  plants  raised  from  seed  sent  me  by 
Dr.  Durando  from  Algiers,  where  the  parent-plants  had  been  cul- 
tivated for  some  generations.  These  latter  plants  differed  in  hav- 
ing pale  pink  instead  of  crimson  flowers,  but  in  no  other  respect. 
That  the  cross  had  been  effective  (though  the  flowers  on  the  crim- 
son mother-plant  had  not  been  castrated)  was  well  shown  when  the 
thirty  crossed  seedlings  flowered,  for  twenty-four  of  them  produced 
pale  pink  flowers,  exactly  like  those  of  their  father ;  the  six  others 
having  crimson  flowers  exactly  like  those  of  their  mother 
and  like  those  of  all  the  self-fertilised  seedlings.  This  case 
offers  a  good  instance  of  a  result  which  not  rarely  follows 
from  crossing  varieties  having  differently  coloured  flowers; 
namely,  that  the  colours  do  not  blend,  but  resemble  perfectly  those 
either  of  the  father  or  mother  plant.  The  seeds  of  both  lots, 
after  germinating  on  sand,  were  planted  on  opposite  sides  of 
eight  pots.  "When  fully  grown,  the  plants  were  measured  to 
the  summits  of  the  flower-heads,  as  shown  in  the  following 
table : — 


106 


IBERIS   UMBELLATA. 


Chap.  IV. 


Table  XXXII. 

Iberis  umbellata :  0  signifies  that  the  Plant  died. 


No.  of  Pot. 

Plants  from  a  Cross 
with  a  fresh  Stock. 

Plants  from  Spon- 
taneously Self-ferti- 
lised Seeds. 

I. 

Inches. 
18| 

17! 
17| 
20 1 

Inches. 
171 
16| 

138 

15| 

II. 

20§ 
151 
17 

0 
16| 
151 

III. 

19| 
18J 

15f 

13| 

141 
13| 

IV. 

17s 

18? 

17  i 

15| 

1*8 

16| 
14| 

16 
15| 

14? 

V. 

18$ 

14? 
161 
15| 
12| 

16§ 
161 
141 
14§ 
16? 

VI. 

18jj 
18| 
17 1 

16? 

15 

15f 

VII. 

18 
16| 

181 

16| 

14;} 
13g 

VIII. 

20 1 

17? 
13| 
191 

15 1 

ief 

20  i 
15g 

Total  in  inches. 

520-38 

449-88 

The  average  height  of   the  thirty  crossed  plants  is    here 
17*34:,  and  that  of  the  twenty-nine  self-fertilised  plants  (one 


Chai\  IV.  PAPAVER  VAGUM.  107 

having  died)  15*51,  or  as  100  to  89.  I  am  surprised  that  the 
difference  did  not  prove  somewhat  greater,  considering  that  in 
the  last  experiment  it  was  as  100  to  86 ;  but  this  latter  ratio,  as 
before  explained,  was  probably  too  great.  In  should,  however, 
be  observed  that  in  the  last  experiment  (Table  XXXI.),  the 
crossed  plants  competed  with  plants  of  the  third  self-fertilised 
generation ;  whilst  in  the  present  case,  plants  derived  from  a 
cross  with  a  fresh  stock  competed  with  self-fertilised  plants  of 
the  first  generation. 

The  crossed  plants  in  the  present  case,  as  in  the  last,  were 
more  fertile  than  the  self-fertilised,  both  lots  being  left  un- 
covered in  the  greenhouse.  The  thirty  crossed  plants  produced 
103  seed-bearing  flower-heads,  as  well  as  some  heads  which 
yielded  no  seeds ;  whereas  the  twenty-nine  self-fertilised  plants 
produced  only  81  seed-bearing  heads;  therefore  thirty  such 
plants  would  have  produced  83*7  heads.  We  thus  get  the 
ratio  of  100  to  81,  for  the  number  of  seed-bearing  flower-heads 
produced  by  the  crossed  and  self -fertilised  plants.  Moreover,  a 
number  of  seed-bearing  heads  from  the  crossed  plants,  com- 
pared with  the  same  number  from  the  self-fertilised,  yielded 
seeds  by  weight,  in  the  ratio  of  100  to  92.  Combining  these 
two  elements,  viz.,  the  number  of  seed-bearing  heads  and  the 
weight  of  seeds  in  each  head,  the  productiveness  of  the  crossed 
to  the  self-fertilised  plants  was  as  100  to  75. 

The  crossed  and  self-fertilised  seeds,  which  remained  after 
the  above  pairs  had  been  planted,  (some  in  a  state  of  germina- 
tion and  some  not  so),  were  sown  early  in  the  year  out  of  doors 
in  two  rows.  Many  of  the  self-fertilised  seedlings  suffered 
greatly,  and  a  much  larger  number  of  them  perished  than  of 
the  crossed.  In  the  autumn  the  surviving  self-fertilised  plants 
were  plainly  less  well-grown  than  the  crossed  plants. 

VII.  PAPAVEKACE^].— Papaver  vagum. 

A  sub-species  of  P.  dubium,  from  the  south  of  France. 

The  poppy  does  not  secrete  nectar,  but  the  flowers  are  highly 
conspicuous  and  are  visited  by  many  pollen-collecting  bees, 
flies  and  beetles.  The  anthers  shed  their  pollen  very  early,  and 
in  the  case  of  P.  rlmas,  it  falls  on  the  circumference  of  the 
radiating  stigmas,  so  that  this  species  must  often  be  self-ferti- 
lised; but  with  P.  dubium  the  same  result  does  not  follow 
(according  to  EL  Miiller, '  Die  Befruchtung,'  p.  128),  owing  to 


108  PAPAVEK  VAGUM.  Chap.  IV, 

the  shortness  of  the  stamens,  unless  the  flower  happens  to  stand 
inclined.  The  present  species,  therefore,  does  not  seem  so  well 
fitted  for  self-fertilisation  as  most  of  the  others.  Nevertheless 
P.  vagum  produced  plenty  of  capsules  in  my  garden  when  insects 
were  excluded,  but  only  late  in  the  season.  I  may  here  add  that 
P.  somnifzrum  produces  an  abundance  of  spontaneously  self- 
fertilised  capsules,  as  Professor  H.  Hoffmann  likewise  found  to 
be  the  case*  Some  species  of  Papaver  cross  freely  when  growing 
in  the  same  garden,  as  I  have  known  to  be  the  case  with  P. 
bracteatum  and  orientale. 

Plant3  of  Papaver  vagum  were  raised  from  seeds  sent  me  from 
Antibes  through  the  kindness  of  Dr.  Bornet.  Some  little  time 
after  the  flowers  had  expanded,  several  were  fertilised  with 
their  own  pollen,  and  others  (not  castrated)  with  pollen  from  a 
distinct  individual ;  but  I  have  reason  to  believe,  from  observa- 
tions subsequently  made,  that  these  flowers  had  been  already 
fertilised  by  their  own  pollen,  as  this  process  seems  to  take  place 
soon  after  their  expansion.!  I  raised,  however,  a  few  seedlings 
of  both  lots,  and  the  self-fertilised  rather  exceeded  the  crossed 
plants  in  height. 

Early  in  the  following  year  I  acted  differently,  and  fertilised 
seven  flowers,  very  soon  after  their  expansion,  with  pollen  from 
another  plant,  and  obtained  six  capsules.  Prom  counting  the 
seeds  in  a  medium-sized  one,  I  estimated  that  the  average 
number  in  each  was  at  least  120.  Pour  out  of  twelve  capsules, 
spontaneously  self-fertilised  at  the  same  time,  were  found  to 
contain  no  good  seeds ;  and  the  remaining  eight  contained  on 
an  average  6*6  seeds  per  capsule.  But  it  should  be  observed 
that  later  in  the  season  the  same  plants  produced  under  a  net 
plenty  of  very  fine  spontaneously  self-fertilised  capsules. 

The  above  two  lots  of  seeds,  after  germinating  on  sand,  were 
planted  in  pairs  on  opposite  sides  of  five  pots.  The  two  Iocs  of 
seedlings,  when  half  an  inch  in  height,  and  again  when  6  inches 
high,  were  measured  to  the  tips  of  their  leaves,  but  presented 


*  'Zur  Speciesfrage,'  1875,  p.  53.  done  "on  the  second  day,  or  even 

f  Mr.  J.  Scott  found  ('  Report  a  few  hours  after  the  expansion 

on  the  Experimental   Culture  of  of  the  flower  on  the  first  day,  a 

the  Opium  Poppy :'  Calcutta,  1874,  partial  fertilisation  had   already 

p.  47),  in  the  case  of  Papaver  som-  been    effected,   and  a  few  good 

"niferum,  that  if  he  cut  away  the  seeds  were  almost  invariably  pro- 

stigmatie     surface     before     the  duced."   This  proves  at  how  early 

flower    had  expanded,    no  seeds  a  period  fertilisation  takes  place, 
were  produced ;  but  if  this  was 


Chap.  IV. 


ESCHSCHOLTZIA   CALIFOKNICA. 


109 


no  difference.  When  fully  grown,  the  flower-stalks  were 
measured  to  the  summits  of  the  seed  capsules,  with  the  follow- 
ing result : — 

Table  XXXILI. 

Papaver  vagum. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

L 

Inches. 
24§ 
30 
18| 

Inches. 
21 
26| 
16 

II. 

14| 
22 
19g 
211 

15| 
20J 
14| 

16S 

III. 

20| 
20 1 
20f 

19 1 

13| 
18 

IV. 

25 1 
24  § 

23 1 
23 

V. 

20 
27  5 
19 

181 

27 

21§ 

Total  in  inches. 

328-75 

293-13 

The  fifteen  crossed  plants  here  average  21  ■  91  inches,  and  the 
fifteen  self-fertilised  plants  19  •  54  inches  in  height,  or  as  100  to 
89.  These  plants  did  not  differ  in  fertility,  as  far  as  could  be 
judged  by  the  number  of  capsules  produced,  for  there  were 
seventy -five  on  the  crossed  side  and  seventy-four  on  the  self- 
fertilised  side. 


ESCHSCHOLTZIA   CALIFOENIOA. 

This  plant  is  remarkable  from  the  crossed  seedlings  not  ex- 
ceeding in  height  or  vigour  the  self-fertilised.  On  the  other 
hand,  a  cross  greatly  increases  the  productiveness  of  the  flowers 
on  the  parent-plant,  and  is  indeed  sometimes  necessary  in  order 
that  they  should  produce  any  seed;  moreover,  plants  thus 
derived  are  themselves  much  more  fertile  than  those  raised  from 


110 


ESCHSCHOLTZIA   CALIFOKNICA. 


Chap.  IV. 


self-fertilised  flowers;  so  that  the  whole  advantage  of  a  cross  is 
confined  to  the  reproductive  system.  It  will  be  necessary  for 
me  to  give  this  singular  case  in  considerable  detail. 

Twelve  flowers  on  some  plants  in  my  flower-garden  were 
fertilised  with  pollen  from  distinct  plants,  and  produced  twelve 
capsules ;  but  one  of  these  contained  no  good  seed.  The  seeds 
of  the  eleven  good  capsules  weighed  17  "4  grains.  Eighteen 
flowers  on  the  same  plants  were  fertilised  with  their  own  pollen 
and  produced  twelve  good  capsules,  which  contained  13  "61 
grains  weight  of  seed.  Therefore  an  equal  number  of  crossed 
and  self-fertilised  capsules  would  have  yielded  seed  by  weight 
as  100  to  71.*  If  we  take  into  account  the  fact  that  a  much 
greater  proportion  of  flowers  produced  capsules  when  crossed 
than  when  self-fertilised,  the  relative  fertility  of  the  crossed  to 
the  self-fertilised  flowers  was  as  100  to  52.  Nevertheless  these 
plants,  whilst  still  protected  by  the  net,  spontaneously  produced 
a  considerable  number  of  self-fertilised  capsules. 

The  seeds  of  the  two  lots  after  germinating  on  sand  were 
planted  in  pairs  on  the  opposite  sides  of  four  large  pots.  At 
first  there  was  no  difference  in  their  growth,  but  ultimately 
the  crossed  seedlings  exceeded  the  self-fertilised  considerably  in 
height,  as  shown  in  the  following  Table.    But  I  believe  from 

Table  XXXIV. 

Esclischoltzia  californica. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
33 1 

Inches. 
25 

II. 

34§ 

35 

III. 

29 

27  § 

IV. 

22 

15 

Total  in  inches. 

118-75 

102-25 

*  Prof.  Hildebrand  experi- 
mented on  plants  in  Germany  on 
a  larger  scale  than  I  did,  and 
found  them  much  more  self-sterile. 
Eighteen  capsules,  produced  by 
cross-fertilisation,  contained  on  an 


average  eighty-five  seeds,  whilst 
fourteen  capsules  from  self-ferti- 
lised flowers  contained  on  an 
average  only  nine  seeds ;  that  is, 
as  100  to  11 :  '  Jahrb,  fur  Wissen. 
Botanik.'    B.  vii.  p.  467. 


Chap.  IV.  ESCHSCHOLTZIA   CALIFOENICA.  Ill 

the  cases  which  follow  that  this  result  was  accidental,  owing  to 
only  a  few  plants  having  been  measured,  and  to  one  of  the 
self-fertilised  plants  having  grown  only  to  a  height  of  15  inches. 
The  plants  had  been  kept  in  the  greenhouse,  and  from  being 
drawn  up  to  the  light  had  to  be  tied  to  sticks  in  this  and  the 
following  trials.  They  were  measured  to  the  summits  of  their 
flower-stems. 

The  four  crossed  plants  here  average  29 '  68  inches,  and  the 
four  self- fertilised  25*56  in  height;  or  as  100  to  86.  The 
remaining  seeds  were  sown  in  a  large  pot  in  which  a  Cineraria 
had  long  been  growing ;  and  in  this  case  again  the  two  crossed 
plants  on  the  one  side  greatly  exceeded  in  height  the  two  self- 
fertilised  plants  on  the  opposite  side.  The  plants  in  the  above 
four  pots  from  having  been  kept  in  the  greenhouse  did  not 
produce  on  this  or  any  other  similar  occasion  many  capsules ; 
but  the  flowers  on  the  crossed  plants  when  again  crossed  were 
much  more  productive  than  the  flowers  on  the  self-fertilised 
plants  when  again  self-fertilised.  These  plants  after  seeding 
were  cut  down  and  kept  in  the  greenhouse;  and  in  the 
following  year,  when  grown  again,  their  relative  heights  were 
reversed,  as  the  self-fertilised  plants  in  three  out  of  the  four 
pots  were  now  taller  than  and  flowered  before  the  crossed 
plants. 

Crosstd  and  seJf-fertib'.S'd  Plants  of  the  Second  Generation. — The 
fact  just  giv/m  with  respect  to  the  growth  of  the  cut-down 
plants  made  me  doubtful  about  my  first  trial,  so  1  determined 
to  make  another  on  a  larger  scale  with  crossed  and  self-fertilised 
seedlings  raised  from  the  crossed  and  self-fertilised  plants  of 
the  last  generation.  Eleven  pairs  were  raised  and  grown  in 
competition  in  the  usual  manner;  and  now  the  result  was 
different,  for  the  two  lots  were  nearly  equal  during  their  whole 
growth.  It  would  therefore  be  superfluous  to  give  a  table  of 
their  heights.  When  fully  grown  and  measured,  the  crossed 
averaged  32 •  47,  and  the  self-fertilised  32 "81  inches  in  height; 
or  as  100  to  101.  There  was  no  great  difference  in  the  number 
of  flowers  and  capsules  produced  by  the  two  lots,  when  both 
wire  left  freely  exposed  to  the  visits  of  insects. 

Plants  raised  from  Brazilian  Seed. — Fritz  Miiller  sent  me  from 
South  Brazil  seeds  of  plants  which  were  there  absolutely 
sterile  when  fertilised  with  pollen  from  the  same  plant,  but 
were  perfectly  fertile  when  fertilised  with  pollen  from  any 
other  plant.  The  plants  raised  by  me  in  England  from  these 
6 


112  ESCHSCHOLTZIA    CALIFOKNICA.  Chai>.  IV. 

needs  were  examined  by  Professor  Asa  Gray,  and  pronounced 
to  belong  to  E.  califorrrica,  with  which,  they  were  identical  in 
general  appearance.  Two  of  these  plants  were  covered  by  a 
net,  and  were  found  not  to  be  so  completely  self- sterile  as  in 
Brazil.  But  I  shall  recur  to  this  subject  in  another  part  of 
this  work.  Here  it  will  suffice  to  state  that  eight  flowers  on 
these  two  plants,  fertilised  with  pollen  from  another  plant 
under  the  net,  produced  eight  fine  capsules,  each  containing  on 
an  average  about  eighty  seeds.  Eight  flowers  on  these  same 
plants,  fertilised  with  their  own  pollen,  produced  seven  capsules, 
which  contained  on  an  average  only  twelve  seeds,  with  a  maxi- 
mum in  one  of  sixteen  seeds.  Therefore  the  cross-fertilised 
capsules,  compared  with  the  self-fertilised,  yielded  seeds  in  the 
ratio  of  about  100  to  15.  These  plants  of  Brazilian  parentage 
differed  also  in  a  marked  manner  from  the  English  plants  in 
producing  extremely  few  spontaneously  self-fertilised  capsules 
under  a  net. 

Crossed  and  self-fertilised  seeds  from  the  above  plants,  after 
germinating  on  bare  sand,  were  planted  in  pairs  on  the  opposite 
sides  of  five  large  pots.  The  seedlings  thus  raised  were  the 
grandchildren  of  the  plants  which  grew  in  Brazil ;  the  parents 
having  been  grown  in  England.  As  the  grandparents  in 
Brazil  absolutely  require  cross-fertilisation  in  order  to  yield 
any  seeds,  I  expected  that  self-fertilisation  would  have  proved 
very  injurious  to  these  seedlings,  and  that  the  crossed  ones 
would  have  been  greatly  superior  in  height  and  vigour  to 
those  raised  from  self-fertilised  flowers.  But  the  result  showed 
that  my  anticipation  was  erroneous;  for  as  in  the  last  experi- 
ment with  plants  of  the  English  stock,  so  in  the  present  one, 
the  self-fertilised  plants  exceeded  the  crossed  by  a  little  in 
height.  It  will  be  sufficient  to  state  that  the  fourteen  crossed 
plants  averaged  44 '  64,  and  the  fourteen  self-fertilised  45  ■  12 
inches  in  height ;  or  as  100  to  101. 

The  Effects  of  a  Cross  with  afresh  Stock. — I  now  tried  a  different 
experiment.  Eight  flowers  on  the  self-fertilised  plants  of  the 
last  experiment  (i.e.,  grandchildren  of  the  plants  which  grew  in 
Brazil)  were  again  fertilised  with  pollen  from  the  same  plant, 
and  produced  five  capsules,  containing  on  an  average  27 '4 
seeds,  with  a  maximum  in  one  of  forty-two  seeds.  The  seedlings 
raised  from  these  seeds  formed  the  second  selffei  tilised  generation 
of  the  Brazilian  stock. 

Eight  flowers  on  one  of  the  crossed  plants  of  the  last  experi- 


Chap.  IV.     CROSS  WITH  A  FRESH  STOCK.        113 

merit  were  crossed  with  pollen  from  another  grandchild,  and 
produced  five  capsules.  These  contained  on  an  average  31  "6 
seeds,  with  a  maximum  in  one  of  forty-nine  seeds.  The  seedlings 
raised  from  these  seeds  may  be  called  the  Intercrossed. 

Lastly,  eight  other  flowers  on  the  crossed  plants  of  the  last 
experiment  were  fertilise!  with  pollen  from  a  plant  of  the 
English  stock,  growing  in  my  garden,  and  which  must  have 
been  exposed  during  many  previous  generations  to  very  different 
conditions  from  those  to  which  the  Brazilian  progenitors  of  the 
mother -plant  had  been  subjected.  These  eight  flowers  produced 
only  fcur  capsules,  containing  on  an  average  63  "2  seeds,  with  a 
maximum  in  one  of  ninety.  The  plants  raised  from  these  seeds 
may  be  called  the  English-crossed.  As  far  as  the  above  averages 
can  be  trusted  from  so  few  capsules,  the  English-crossed  capsules 
contained  twice  as  many  seeds  as  the  intercrossed,  and  rather 
more  than  twice  as  many  as  the  self-fertilised  capsules.  The 
plants  which  yielded  these  capsules  were  grown  in  pots  in  the 
greenhouse,  so  that  their  absolute  productiveness  must  not  be 
compared  with  that  of  plants  growing  out  of  doors. 

The  above  three  lots  of  seeds,  viz.,  the  self  fertilised,  inter- 
crossed, and  English-crossed,  were  planted  in  an  equal  state  of 
germination  (having  been  as  usual  sown  on  bare  sand)  in  nine 
large  pots,  each  divided  into  three  parts  by  superficial  partitions. 
Many  of  the  self-fertilised  seeds  germinated  before  those  of  the 
two  crossed  lots,  and  these  were  of  course  rejected.  The 
seedlings  thus  raised  are  the  great-grandchildren  of  the  plants 
which  grew  in  Brazil.  When  they  were  from  2  to  4  inches 
in  height,  the  three  lots  were  equal.  They  were  measured  when 
four-fifths  grown,  and  again  when  fully  grown,  and  as  their 
relative  heights  were  almost  exactly  the  same  at  these  two 
ages,  I  will  give  only  the  last  measurements.  The  average 
height  of  the  nineteen  English-crossed  plants  was  45 '  92  inches ; 
that  of  the  eighteen  intercrossed  plants  (for  one  died),  43  "38; 
and  that  of  the  nineteen  self- fertilised  plants,  50  "3  inches.  So 
that  we  have  the  following  ratios  in  height : — 

The  English-crossed  to  the  self-fertilised  plants,  as  100  to  109 
The  English-crossed  to  the  intercrossed  plants,  as  100  to  94 
The    intercrossed    to  the  self- fertilised  plants,  as  100  to  116 

After  the  seed-capsules  had  been  gathered,  all  these  plants 
were  cat  down  close  to  the  ground  and  weighed.  The  nineteen 
English  crossed  plan's  weighed  18r25  ounces;  the  intercrossed 


114  ESCHSCHOLTZIA   CALIFOENICA.  Chap.  IV. 

plants  (with  their  weight  calculated  as  if  there  had  been  nine- 
teen) weighed  18 '2  ounces;  and  the  nineteen  self-fertilised 
plants,  21*5  ounces.  "We  have  therefore  for  the  weights  of  the 
three  lots  of  plants  the  following  ratios  : — 

The  English-crossed  to  the  self- fertilised  plants,  as  100  to  118 
The  English-crossed  to  the  intercrossed  plants,  as  100  to  100 
The  intercrossed  to  the  self-fertilised  plants,  as  100  to  118 

We  thus  see  that  in  weight,  as  in  height,  the  self-fertilised 
plants  had  a  decided  advantage  over  the  English-crossed  and 
intercrossed  plants. 

The  remaining  seeds  of  the  three  kinds,  whether  or  not  in  a 
state  of  germination,  were  sown  in  three  long  parallel  rows  in 
the  open  ground;  and  here  again  the  self-fertilised  seedlings 
exceeded  in  height  by  between  2  and  3  inches  the  seedlings 
in  the  two  other  rows,  which  were  of  nearly  equal  heights.  The 
three  rows  were  left  unprotected  throughout  the  winter,  and  all 
the  plants  were  killed,  with  the  exception  of  two  of  the  self- 
fertilised  ;  so  that  as  far  as  this  little  bit  of  evidence  goes,  some 
of  the  self-fertilised  plants  were  more  hardy  than  any  of  the 
crossed  plants  of  either  lot. 

We  thus  see  that  the  self- fertilised  plants  which  were  grown 
in  the  nine  pots  were  superior  in  height  (as  116  to  100),  and  in 
weight  (as  118  to  100),  and  apparently  in  hardiness,  to  the  inter- 
crossed plants  derived  from  a  cross  between  the  grandchildren 
of  the  Brazilian  sto^k.  The  superiority  is  here  much  more 
stroDgly  marked  than  in  the  second  trial  with  the  plants  of  the 
English  stock,  in  which  the  self-fertilised  were  to  the  crossed  in 
height  as  101  to  100.  It  is  a  far  more  remarkable  fact — if  we 
bear  in  mind  the  effects  of  crossing  plants  with  pollen  from  a 
fresh  stock  in  the  cases  of  Ipomoea,  Mimulus,  Brassica,  and 
Iberis— that  the  self-fertilised  plants  exceeded  in  height  (as  109 
to  100),  and  in  weight  (as  118  to  100),  the  offspring  of  the 
Brazilian  stock  crossed  by  the  English  stock;  the  two  stocks 
having  been  long  subjected  to  widely  different  conditions. 

If  we  now  turn  to  the  fertility  of  the  three  lots  of  plants  we 
find  a  very  different  result.  1  may  premise  that  in  five  out  of 
the  nine  pots  the  first  plant  which  flowered  was  one  of  the  English- 
crossed  ;  in  four  of  the  pots  it  was  a  self  fertilised  plant;  and  in 
not  one  did  an  intercrossed  plant  flower  first;  so  that  theso 
latter  plants  were  beaten  in  this  respect,  as  in  so  many  other 
ways.     The  three  closely  adjoining  rows  of  plants  growing  in 


Chap.  IV.  CROSS   WITH  A  FEESH   STOCK.  115 

the  open  ground  flowered  profusely,  and  the  flowers  were  inces- 
santly visiled  by  bees,  and  certainly  thus  intercrossed.  The 
manner  in  which  several  plants  in  the  previous  experiments 
continued  to  be  almost  sterile  as  long  as  they  were  covered  by  a 
net,  but  set  a  multitude  of  capsules  immediately  that  they  were 
uncovered,  proves  how  effectually  the  bees  carry  pollen  from 
plant  to  plant.  My  gardener  gathered,  at  three  successive 
times,  an  equal  number  of  ripe  capsules  from  the  plants  of  the 
three  lots,  until  he  had  collected  forty-five  from  each  lot.  It  is 
not  possible  to  judge  from  external  appearance  whether  or  not  a 
capsule  contains  any  good  seeds ;  so  that  I  opened  all  the  cap- 
sules. Of  the  forty-five  from  the  English-crossed  plants,  four 
were  empty ;  of  those  from  the  intercrossed,  five  were  empty  ; 
and  of  those  from  the  self-fertilised,  nine  were  empty.  The 
seeds  were  counted  in  twenty-one  capsules  taken  by  chance  out 
of  each  lot,  and  the  average  number  of  seeds  in  the  capsules 
from  the  English-crossed  plants  was  67 ;  from  the  intercrossed, 
56 ;  and  from  the  self- fertilised,  48 '52.    It  therefore  follows  that 

Seeds. 

The  forty-five  capsules  (the  four  empty  ones  in- 
cluded) from  the  English-crossed  plants  contained     2747 

The  forty-five  capsules  (the  five  empty  ones  in- 
cluded) from  the  intercrossed  plants  contained       .     2240 

The  forty-five  capsules  (the  nine  empty  ones  in- 
cluded) from  the  self-fertilised  plants  contained     .     1746  ■  7 

The  reader  should  remember  that  these  capsules  are  the  pro- 
duct of  cross-fertilisation,  effected  by  the  bees;  and  that  the 
difference  in  the  number  of  the  contained  seeds  must  depend  on 
the  constitution  of  the  plants ; — that  is,  on  whether  they  were 
derived  from  a  cross  with  a  distinct  stock,  or  from  a  cross 
between  plants  of  the  same  stock,  or  from  self-fertilisation. 
From  the  above  facts  we  obtain  the  following  ratios : — 

Number  of  seeds  contained  in  an  equal  number  of  naturally 
fertilised  capsules  produced — 

By  the  English-crossed  and  self-fertilised  plants,  as  100  to  63 
By  the  English-crossed  and  intercrossed  plants,  as  100  to  81 
By  the  intercrossed  and  self-fertilised  plants,         as  100  to  78 

But  to  have  ascertained  the  productiveness  of  the  three  lots 
of  plants,  it  would  have  been  necessary  to  know  how  many 
capsules  were  produced  by  the  same  number  of  plants.    The 


116  ESCHSCKOLTZIA   CALIFOKNICA.  Chap.  IV. 

three  long  rows,  however,  were  not  of  quite  equal  lengths,  and 
the  plants  were  much  crowded,  so  that  it  would  have  been  ex- 
tremely difficult  to  have  ascertained  how  many  capsules  were 
produced  by  them,  even  if  I  had  been  willing  to  undertake  so 
laborious  a  task  as  to  collect  and  count  all  the  capsules.  But 
this  was  feasible  with  the  plants  grown  in  pots  in  the  green- 
house; and  although  these  were  much  less  fertile  than  those 
growing  out  of  doors,  their  relative  fertility  appeared,  after  care- 
fully observing  them,  to  be  the  same.  The  nineteen  plants  of 
the  English-crossed  stock  in  the  pots  produced  altogether  210 
capsules;  the  intercrossed  plants  (calculated  as  nineteen)  pro- 
duced 137"22  capsules;  and  the  nineteen  self-fertilised  plants, 
152  capsules.  Nuw,  knowing  the  number  of  seeds  contained  in 
forty-five  capsules  of  each  lot,  it  is  easy  to  calculate  the  relative 
numbers  of  seeds  produced  by  an  equal  nixmber  of  the  plants  of 
the  three  lots. 

Number  of  seeds  produced  by  an  equal  number  of  naturally- 
fertilised  plants. 

Seeds. 
Plants  of  English-crossed    and    self-feitilised 
parentage  .......      as  100  to  10 

Plants  of  the  English-crossed  and  intercrossed 

parentage  .......      as  100  to  45 

Plants  of  the  intercrossed  and  self-fertilised 
parentage as  100  to  89 

The  superiority  in  productiveness  of  the  intercrossed  plants 
(that  is,  the  product  of  a  cross  between  the  grandchildren  of  the 
plants  which  grew  in  Brazil)  over  the  self-fertilised,  small  as  it  is, 
is  wholly  due  to  the  larger  average  number  of  seeds  contained  in 
the  capsules;  for  the  intercrossed  plants  produced  fewer  cap- 
sules in  the  greenhouse  than  did  the  self-fertilised  plants.  The 
great  superiority  in  productiveness  of  the  English-crossed  over 
the  self-fertilised  plants  is  shown  by  the  larger  number  of 
capsules  produced,  the  larger  average  number  of  contained  seeds, 
and  the  smaller  number  of  empty  capsules.  As  the  English- 
crossed  and  intercrossed  plants  were  the  offspring  of  crosses  in 
every  previous  generation  (as  must  have  been  the  case  froin  the 
flowers  being  sterile  with  their  own  pollen),  we  may  conclude  that 
the  great  superiority  in  productiveness  of  the  English-crossed 
over  the  intercrossed  plants  is  due  to  the  two  parents  of  the 
former  having  been  long  subjected  to  different  conditions. 


CnAr.  IV.  EESEDA   LUTEA.  117 

The  English-crossed  plants.,  though  so  superior  in  productive- 
ne?s,  were,  as  we  have  seen,  decidedly  inferior  in  height  and 
weight  to  the  self-fertilised,  and  only  equal  to,  or  hardly  superior 
to,  the  intercrossed  plants.  Therefore,  the  whole  advantage  of  a 
cross  with  a  distinct  stock  is  here  confined  to  productiveness,  and 
I  have  met  with  no  similar  case. 

VIII.  EESEDACEiE.— Eeseda  ltjtea. 

Seeds  collected  from  wild  plants  growing  in  this  neighbour- 
hood were  sown  in  the  kitchen- garden ;  and  several  of  the 
seedlings  thus  raised  were  covered  with  a  net.  Of  these,  some 
were  found  (as  will  hereafter  be  more  fully  described)  to  be 
absolutely  sterile  when  left  to  fertilise  themselves  spontaneously, 
although  plenty  of  pollen  fell  on  their  stigmas ;  and  they  were 
equally  sterile  when  artificially  and  repeatedly  fertilised  with 
their  own  pollen ;  whiUt  other  plants  produced  a  few  spon- 
taneously self- fertilised  capsxiles.  The  remaining  plants  were 
left  uncovered,  and  as  pollen  was  carried  from  plant  to  plant  by 
the  hive  and  humble-bees  which  incessantly  visit  the  flowers, 
they  produced  an  abundance  of  capsules.  Of  the  necessity  of 
pollen  being  carried  from  one  plant  to  another,  I  had  ample 
evidence  in  the  case  of  this  species  and  of  JR.  odorata ;  for  those 
plants,  which  set  no  seeds  or  very  few  as  long  as  they  were 
protected  from  insects,  became  loaded  with  capsules  immediately 
that  they  were  uncovered. 

Seeds  from  the  flowers  spontaneously  self  fertilised  under  the 
net,  and  from  flowers  naturally  crossed  by  the  bees,  were  sown  on 
opposite  sides  of  five  large  pots.  The  seedlings  were  thinned  as 
soon  as  they  appeared  above  ground,  so  that  an  equal  nuruber 
were  left  on  the  two  sides.  After  a  time  the  pots  were  plunged 
into  the  open  gtound.  The  same  number  of  plants  of  crossed 
and  self- fertilised  parentage  were  measured  up  to  the  summits 
of  their  flower-stems,  with  the  result  given  in  the  following 
table  (XXXV.).  Those  which  did  not  produce  flower-stems  were 
not  measured. 

The  average  height  of  the  twenty-four  crossed  plants  is  here 
17 '17  inches,  and  that  of  the  same  number  of  self- fertilised  plants 
14  "61;  or  as  100  to  85.  Of  the  crossed  plan's  all  but  five 
flowered,  whilst  several  of  the  self-fertilised  did  not  do  so.  The 
above  pairs,  whilst  still  in  flower,  but  with  some  capsules  already 
formed,  were  afterwards  cut  down,  and  weighed.    The  crossed 


118 


RESEDA   LUTEA. 


Chap.  IV. 


weighed  90 "  5  ounces ;  and  an  equal  number  of  the  self-fertilised 
only  19  ounces,  or  as  100  to  21;  and  this  is  an  astonishing 
difference. 

Table  XXXV. 
Beseda  lutea,  in  pots. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

Inches. 

Inches. 

I. 

21 

121 

W  § 

16 

19£ 

7 

HI 
15§ 

15* 

19£ 

II. 

20| 

12| 

17| 

16| 

231 

17^ 
20| 

16§ 
13  j 

13| 

III. 

16J 

14| 

17| 
16| 

10 

19| 

201 
7? 

10 

17| 

IV. 

99  I 

9 

19 

HI 

18? 

11 

16| 

16 

19f 

161 

V. 

25| 

14f 

22 

16 

8| 

14| 

14§ 
1^1 

Total  in  inches. 

412-25 

350-86 

Seeds  of  the  same  two  lots  were  also  sown  in  two  adjoining 
rows  in  the  open  ground.  There  were  twenty  crossed  plants  in 
the  one  row  and  thirty-two  self-fertilised  plants  in  the  other 
row,  so  that  the  experiment  was  not  quite  fair ;  but  not  so  un- 
fair as  it  at  first  appears,  for  the  plants  in  the  same  row  were  not 
crowded  so  much  as  seriously  to  interfere  with  each  other's 
growth,  and  the  ground  was  bare  on  the  outside  of  both  rows. 


Chap.  IV. 


RESEDA    ODORATA. 


119 


These  plants  were  better  nourished  than  those  in  the  pots  and 
grew  to  a  greater  height.  The  eight  tallest  plants  in  each  row 
were  measured  in  the  same  manner  as  before,  with  the  following 
result : — 

Table  XXXVI. 

Reseda  lutea,  growing  in  the  open  ground. 


Crossed  Plants. 

Self-fertilised  Plants. 

Inches 
28 
27  § 
27  § 
28 1 
29 1 
26  § 
26 1 

so  4 

Inches. 
33  § 
23 
21 1 
20| 

21 1 
22 

211 
211 

224-75 

185-13 

The  average  height  of  the  crossed  plants,  whilst  in  full  flower, 
was  here  28'09,  and  that  of  the  self-fertilised  23  14  inches ;  or  as 
100  to  82.  It  is  a  singular  fact  that  the  tallest  plant  in  the  two 
rows,  was  one  of  the  self-fertilised.  The  self-fertilised  plants  had 
smaller  and  paler  green  leaves  than  the  crossed.  All  the  pLmts 
in  the  two  rows  were  afterwards  cut  down  and  weighed.  The 
twenty  crossed  plants  weighed  65  ounces,  and  twenty  self-ferti- 
lised (by  calculation  from  the  actual  weight  of  the  thirty-two  self- 
fertilised  pUnts)  weighed  26  ■  25  ounces ;  or  as  100  to  40.  There- 
fore the  crossed  plants  did  not  exceed  in  weight  the  self-fertilised 
plants  in  nearly  so  great  a  degree  as  those  growing  in  the 
pots,  owing  probably  to  the  latter  having  beeu  subjected  to  more 
severe  mutual  competition.  On  the  other  hand,  they  exceeded 
the  self-fertilised  in  height  in  a  slightly  greater  degree. 


EESEDA   ODORATA. 

Plants  of  the  common  mignonette  were  raised  from  purchased 
seed,  and  several  of  them  were  placed  under  separate  nets.  Of 
these  some  became  loaded  with  spontaneously  t-elf-fertilised  cap- 
sules; others  produced  a  few,  and  others  not  a  single  one.  It 
must  not  be  supposed  that  these  latter  plants  produced  no  seed 


120 


EESEDA   ODOEATA. 


Chap.  IV. 


because  their  stigmas  did  not  receive  any  pollen,  for  they  were 
repeatedly  fertilised  with  pollen  from  the  same  plant  with  no 
sffect ;  but  they  were  perfectly  fertile  with  pollen  from  any  other 
plant^  Spontaneously  self-fertilised  seeds  were  saved  from  one 
of  the  highly  self-fertile  plants,  and  other  seeds  were  collected 
from  the  plants  growiug  outside  the  nets,  which  had  been 
crossed  by  the  bees.  These  seeds  after  germinatiDg  on  sand 
were  planted  in  pairs  on  the  opposite  sides  of  five  pots.  The 
plants  were  trained  up  sticks,  and  measured  to  the  summits  of 
their  leafy  stems — the  flower-stems  not  being  included.  We  hero 
have  the  result : — 

Table  XXXVII. 
Ee?eda  odorata  (seedlings  from,  a  highly  Self-fertile  Plant) 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

Inches. 

Inches. 

I. 

201 

22 1 

34 1 

28 1 

26 1 

23§ 

32« 

30 1 

II. 

34  § 

28| 

34| 

30 1 

Hf 

23 

33 1 

30| 

III. 

171 

4I 

27 

25 

30 1 

26 1 

30 1 

25 1 

IV. 

21§ 

22 1 

28 

25  i 

32 1 

151 

32f 

24§ 

V. 

21 

HI 

25§ 

19  J 

26§ 

10| 

Total  in  inches. 

522-25 

428-50 

The  average  height  of  the  nineteen  crossed  plants  is  here 
27  "48,  and  that  of  the  nineteen  self-fertilised  22*55  inches ;  or  as 
100  to  82.    All  these  plants  were  cut  down  in  the  early  autumn 


Chap.  IV. 


EESEDA    ODORATA. 


121 


and  weighed  :  the  crossed  weighed  11  "5  ounces,  and  the  self- 
fertilised  7 '75  ounces  or  as  100  to  67.  These  two  lots  having 
been  left  freely  exposed  to  the  visits  of  insects,  did  not  present 
any  difference  to  the  eye  in  the  number  of  seed-capsules  which 
they  produced. 

The  remainder  of  the  same  two  lots  of  seeds  were  sown  in  two 
adjoining  rows  in  the  open  ground  ;  so  that  the  plants  were  ex- 
posed to  only  moderate  competition.  The  eight  tallest  on  each 
side  were  measured,  as  shown  in  the  following  table  : — 

Table  XXXVIII. 

Reseda  odorata,  growing  in  the  open  ground. 


Crossed  Plants. 

Self-fertilised  Plants. 

Inches. 

Inches. 

24  jj 
27 1 
24 

26 1 
25 

26 1 
25 

281 
291 

26 1 
27§ 
25£ 

251 
261 
28§ 

Total  in')  OA„  .  10 
inches.^206   13 

216-75 

The  average  height  of  the  eight  crossed  plants  is  25*  76,  and 
that  of  the  eight  self-fertilised  27'09  ;  or  as  100  to  105. 

We  here  have  the  anomalous  result  of  the  self  fertilised  plants 
being  a  little  taller  than  the  crossed ;  of  which  fact  I  can  offer 
no  explanation.  It  is  of  course  possible,  but  not  probable,  that 
the  labels  may  have  been  interchanged  by  accident. 

Another  experiment  was  now  tried :  all  the  self- fertilised 
capsules,  though  very  few  in  number,  were  gathered  from  one  of 
the  semi-self-sterile  plants  under  a  net ;  and  as  several  flowers  on 
this  same  plant  had  been  fertilised  with  pollen  from  a  distinct 
individual,  crossed  seeds  were  thus  obtained.  I  expected  that  the 
seedlings  from  this  semi-self-sterile  plant  would  have  profited 
in  a  higher  degree  from  a  cross,  than  did  the  seedlings  from 
the  fully  self-fertile  plants.  But  my  anticipation  was  quite  wrong, 
for  they  profited  in  a  less  degree.  An  analogous  result  followed  in 
the  case  of  Eschscholtzia,  in  which  the  offspring  of  the  plants  of 
Brazilian  parentage  (which  were  partially  self-sterile)  did  not 


122 


RESEDA   ODORATA. 


Chap.  IV. 


profit  more  from  a  cross,  than  did  the  plants  of  the  far  more 
self-fertile  English  stock.  The  above  two  lots  of  crossed  and 
self-fertilised  seeds  from  the  same  plant  of  Reseda  odorata,  after 
germinating  on  sand,  were  planted  on  opposite  sides  of  five  potSj 
and  measured  as  in  the  last  case,  with  the  following  result : — ■ 


Table  XXXIX. 
Reseda  odorata  (seedlings  from  a  semi-self-sterile  Planf). 


No.  of  Pot. 

Crossed  Plants. 

Seif-fertilised  Plants. 

I. 

Inches. 
33 1 
30 1 
29| 
20 

Inches. 
31 
28 
13§ 

32 

II. 

22 
33 1 
31| 
32 1 

21 1 
26 1 
25| 
80* 

III. 

30 1 
32  J 
31 1 
32| 

171 
29 1 
24§ 
34| 

17. 

19B 

30 1 
243 
30| 

20 1 
32 1 

si  i 

36 1 

V. 

34  g 

37  J 
31 1 
33 

24f 

34 
22| 
37 1 

Total  in  inches. 

599-75 

554-25 

The  average  height  of  the  twenty  crossed  plants  is  here  29-98, 
and  that  of  the  twenty  self- fertilised  27 "71  inches;  or  as  100  to 
92.  These  plants  were  then  cut  down  and  weighed ;  and  the 
crossed  in  this  case  exceeded  the  self-fertilised  in  weight  by  a  mere 
trifle,  viz.,  in  the  ratio  of  100  to  99.  The  two  lots,  left  freely 
exposed  to  insects,  seemed  to  be  equally  fertile. 

The  remainder  of  the  seed  was  sown  in  two  adjoining  rows  in 


Chap.  IV. 


VIOLA   TEICOLOE. 


123 


the  open  ground  ;  and  the  eight  tallest  plants  in  each  row  were 
measured,  with  the  following  result : — 

Table  XL. 

Reseda  odorata  (seedlings  from  a  semi-self-sterile  Plant,  planted 

in  the  open  ground). 


Crossed  Plants. 

Self-fertilised  Plants. 

Inches. 

28  jj 
22) 
25g 

25 1 

29  j 
27 1 
22| 
26f 

Inches. 
22  i 
24 1 
23 1 
21| 

995 

27 1 
27 1 
19§ 

inches.  £207'  38 

188-38 

The  average  height  of  the  eight  crossed  plants  is  here  25 "  92, 
and  that  of  the  eight  self-fertilised  plants  23 '  54  inches ;  or  as 
100  to  90. 

IX.  YIOLACEJ3.— Viola  tricolor. 

Whilst  the  flowers  of  the  common  cultivated  heartsease  are 
young,  the  anthers  shed  their  pollen  into  a  little  semi-cylin- 
drical passage,  formed  by  the  basal  portion  of  the  lower  petal, 
and  surrounded  by  papillae.  The  pollen  thus  collected  lies 
close  beneath  the  stigma,  but  can  seldom  gain  access  into  its 
cavity,  except  by  the  aid  of  insects,  which  pass  their  proboscides 
down  this  passage  into  the  nectary.*  Consequently  when  I 
covered  up  a  large  plant  of  a  cultivated  variety,  it  set  only 
eighteen  capsules,  and  most  of  these  contained  very  few  good 
seeds — several  from  only  one  to  three;  whereas  an  equally  fine 


*  The  flowers  of  this  plant 
have  been  fully  described  by 
Sprengel,  Hildcrand,  Delpino, 
and  H  Midler.  The  latter  author 
sums  up  a.l  the  previous  ob.er- 
vations  in  bis  '  Bei'nichtung  der 
Blunien,'  and  in  -Nature,'  Nov. 
20, 1873,  p.  14.  See  also  Mr.  A.  W. 


Bennett,  in  'Nature,'  May  15, 
1873,  p.  50;  and  some  remarks 
by  Mr.  Kitchener,  ibid.  p.  143. 
The  facts  which  follow  on  the 
effects  of  cov'  ring  up  a  plant 
of  V.  tricolor  have  been  quoted 
by  Sir  J.  Lulibock  in  his  'British 
Wild  Flowers,'  &c.  p.  62. 


124  VIOLA  TRICOLOR.  Chap.  IV. 

uncovered  plant  ot  the  same  variety,  growing  close  by,  produced 
105  fine  capsules.  The  few  flowers  which  produce  capsules  when 
insects  are  excluded,  are  perhaps  fertilised  by  the  curling  inwards 
of  the  petals  as  they  wither,  for  by  this  means  pollen- grains 
adhering  to  the  papillae  might  be  inserted  into  the  cavity  of  the 
stigma.  But  it  is  more  probable  that  their  fertilisation  is  effected, 
as  Mr.  Bennett  suggests,  by  Thrips  and  certain  minute  beetles 
which  haunt  the  flowers,  and  which  cannot  be  excluded  by  any 
net.  Humble-bees  are  the  usual  fertilisers ;  but  I  have  more  than 
once  seen  flies  (Rhinyia  rostrata)  at  work,  with  the  under  sides  of 
their  bodies,  heads  and  legs  dusted  with  pollen;  and  having 
marked  the  flowers  which  they  visited,  I  found  them  after  a  few 
days  fertilised.*  It  is  curious  for  how  long  a  time  the  flowers  of 
the  heartsease  and  of  some  other  plants  may  be  watched  without 
an  insect  being  seen  to  visit  them.  During  the  summer  of  1841, 1 
observed  many  times  daily  for  more  than  a  fortnight  some  large 
clumps  of  heartsease  growing  in  my  garden,  before  I  saw  a  single 
humble-bee  at  work.  During  another  summer  I  did  the  same,  but 
at  last  saw  some  dark-coloured  humble-bees  visiting  on  three  suc- 
cessive days  almost  every  flower  in  several  clumps ;  and  almost 
all  these  flowers  quickly  withered  and  produced  fine  capsules. 
I  presume  that  a  certain  state  of  the  atmosphere  is  necessary 
for  the  secretion  of  nectar,  and  that  as  soon  as  this  occurs  the 
insects  discover  the  fact  by  the  odour  emitted,  and  immediately 
frequent  the  flowers. 

As  the  flowers  require  the  aid  of  insects  for  their  complete 


*  I   should   add  that   this   fly  of  these  bees  doing  so.    H.  Miiller 

apparently  did  not  suck  the  nee-  his  also  seen  the  hive-bee  at  work, 

tar,  but  was  attracted  by  the  pa-  but    only    on    the    wild     srnall- 

pillffi  which  surround  the  stigma.  flowered  form.      He  gives  a  list 

H.  Miider  al-o  saw  a  small  bee,  an  ('Nature,'  1873,  p  45)  of  all  the 

Andiena,  which  could  not  reach  insects  which  he  has  seen  visiting 

the  nectar,   repeatedly  inserting  both  the  large  and  ^mall-flowered 

its  proboscis  beneath  the  stigma,  forms.     From  his  account,  I  sus- 

where   the  papilla?  are  situated ;  pect  that  the  flowers  of  plants  in 

so  that  the.se  papillae  must  be  in  a  state  of  nature  are  visited  more 

si  mie  way  attractive  to  insects.   A  frequently  by  insects  than  those 

writer  asserts  ('  Zoologist,'   vol.  of  the   cultivated   varieties.     He 

iii.-iv.    p.    1225)    that    a    moth  has  seen  several  butterflies  suck- 

(Plusia)    frequently   visits     the  ing   the  flowers   of  wild    plants, 

flowers  of  the  pansy.     Hive  bet-s  and  this  I  have  never  observed  in 

do  not  ordinardy  \isit  them,  but  gnidens,  tnough  I  have  watched 

a  case  has  been  recorded  ('Gar-  the  flowers  during  many  years, 
deners'  Cliroaicle,'  1844,  p.  374) 


Chap.  IV.  VIOLA  TEICOLOK.  J  25 

fertilisation,  and  as  they  are  not  visited  by  insects  nearly  so  often 
as  most  other  nectar-secreting  flowers,  we  can  understand  the 
remarkable  fact  discovered  by  H.  Miiller  and  described  by  him 
in  '  Nature/  namely,  that  this  species  exists  under  two  forms. 
One  of  these  bears  conspicuous  flowers,  which,  as  we  have  seen, 
require  the  aid  of  insects,  and  are  adapted  to  be  cross-fer- 
tilised by  them ;  whilst  the  other  form  has  much  smaller  and 
less  conspicuously  coloured  flowers,  which  are  constructed  on  a 
slightly  different  plan,  favouring  self-fertilisation,  and  are  thus 
adapted  to  ensure  the  propagation  of  the  species.  The  self- 
fertile  form,  however,  is  occasionally  visited,  and  may  be  crossed 
by  insects,  though  this  is  rather  doubtful. 

In  my  first  experiments  on  Viola  tricolor  I  was  unsuccessful  in 
raising  seedlings,  and  obtained  only  one  full-grown  crossed  and 
self-fertilised  plant.  The  former  was  12k  inches  and  the  latter  8 
inches  in  height.  On  the  following  year  several  flowers  on  a 
fresh  plant  were  crossed  with  pollen  from  another  plant,  which 
was  known  to  be  a  distinct  seedling ;  and  to  this  point  it  is  im- 
portant to  attend.  Several  other  flowers  on  the  same  plant 
were  fertilised  with  their  own  pollen.  The  average  number 
of  seeds  in  the  ten  crossed  capsules  was  18  "7,  and  in  the  twelve 
self-fertilised  capsules  12  ■  83 ;  or  as  100  to  69.  These  seeds, 
after  germinating  on  bare  sand,  were  planted  in  pairs  on  tho 
opposite  sides  of  five  pots.  They  were  first  measured  when 
about  a  third  of  their  full  size,  and  the  crossed  plants  then 
averaged  3  "87  inches,  and  the  self-fertilised  only  2*00  inches  in 
height ;  or  as  100  to  52.  They  were  kept  in  the  greenhouse,  and 
did  not  grow  vigorously.  Whilst  in  flower  they  were  again 
measured  to  the  summits  of  their  stems  (see  Table  XLI.),  with 
the  following  result : — 

The  average  height  of  the  fourteen  crossed  plants  is  here  5 "  58 
inches,  and  that  of  the  fourteen  self-fertilised  2-37;  or  as  100  to 
42.  In  four  out  of  the  five  pots,  a  crossed  plant  flowered  before 
any  one  of  the  self-fertilised  ;  as  likewise  occurred  with  the  pair 
raised  during  the  previous  year.  These  plants  without  being 
disturbed  were  now  turned  out  of  their  pots  and  planted  in  the 
open  ground,  so  as  to  form  five  separate  clumps.  Early  in  the 
following  summer  (1869)  they  flowered  profusely,  and  being 
visited  by  humble-bees  set  many  capsules,  which  were  carefully 
collected  from  all  the  plants  on  both  sides.  The  crossed  plants 
produced  167  capsules,  and  the  self-fertilised  only  17 ;  or  as 
100  to  10.    So  that  the  crossed  plants  were  more  than  twice  the 


126 


VIOLA   TEICOLOE. 


Chap.  IV. 


height  of  the  self-fertilised,  generally  flowered  first,  and  produced 
ten  times  as  many  naturally  fertilised  capsules. 

Table  XLI. 

Viola  tricolor. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 

R2 

7  4 
•  3 

5 

Inches. 
02 

vs 

94 

1  2 
l9 

II. 

5 

4 
4< 

6 

4 

III. 

9§ 
8| 

8'1 

Of 

IV. 

4.2 

4 

9  ' 

1|       . 
2S 

V. 

6 

Q3 

^8 

3 
1  * 

Total  in  inches. 

78-13 

33-25 

By  the  early  part  of  the  summer  of  1870  the  crossed  plants  in 
all  the  five  clumps  had  grown  and  spread  so  much  more  than 
the  self-fertilised,  that  any  comparison  between  them  was 
superfluous.  The  crossed  plants  were  covered  with  a  sheet  of 
bloom,  whilst  only  a  single  self-fertilised  plant,  which  was  much 
finer  than  any  of  its  brethren,  flowered.  The  crossed  and  self- 
fertilised  plants  had  now  grown  all  matted  together  on  the 
respective  sides  of  the  superficial  partitions  still  separating  them ; 
and  in  the  clump  which  included  the  fine-t  self-fertilised  plant, 
I  estimated  that  the  surface  covered  by  the  crossed  plants  was 
about  nine  times  as  large  as  that  covered  by  the  self-fertilised 
plants.  The  extraordinary  superiority  of  the  crossed  over  the 
self-fertilised  plants  in  all  five  clumps,  was  no  doubt  due  to 
the  crossed  plants  at  first  having  had  a  decided  advantage  over 
the  self-fertilised,  and  then  robbing  them  more  and  more  of  their 
food  during  the  succeeding  seasons.     But  we  should  remember 


Chap.  IV. 


VIOLA   TEICOLOK. 


127 


that  the  same  result  would,  follow  in  a  state  of  nature  even  to  a 
greater  degree ;  for  my  plants  grew  in  ground  kept  clear  of 
weeds,  so  that  the  self-fertilised  had  to  compete  only  with  the 
crossed  plants;  whereas  the  whole  surface  of  the  ground  is 
naturally  covered  with  various  kinds  of  plants,  all  of  which 
have  to  struggle  together  for  existence. 

The  ensuing  winter  was  very  severe,  and  in  the  following 
spring  (1871)  the  plants  were  again  examined.  All  the  self- 
fertilised  were  now  dead,  with  the  exception  of  a  single  branch  on 
one  plant,  which  bore  on  its  summit  a  minute  rosette  of  leaves 
about  as  large  as  a  pea.  On  the  other  hand,  all  the  crossed 
plants  without  exception  were  growing  vigorously.  So  that  the 
self-fertilised  plants,  besides  their  inferiority  in  other  respects, 
were  more  tender. 

Another  experiment  was  now  tried  for  the  sake  of  ascertaining 
how  far  the  superiority  of  the  crossed  plants,  or  to  speak  more 
correctly,  the  inferiority  of  the  self-fertilised  plants,  would  be 
transmitted  to  their  offspring.  The  one  crossed  and  one  self- 
fertilised  plant,  which  were  first  raised,  had  been  turned  out  of 
their  pot  and  planted  in  the  open  ground.  Both  produced  an 
abundance  of  very  fine  capsules,  from  which  fact  we  may  safely 
conclude  that  they  had  been  cross-fertilised  by  insects.  Seeds 
from  both,  after  germinating  on  sand,  were  planted  in  pairs  on 
the  opposite  sides  of  three  pots.     The  naturally  crossed  seedlings 


Table  XLII. 

Viola  tricolor:  seedlings  from  crosstd  and  self-fertilised  Plants,  the 

parents  of  both  sets  having  been  left  to  be  naturally  feitilised. 


No.  of  Pot. 

Naturally  crossed 
riants  from  artifi- 
cially crossed  Plants. 

Naturally  crossed 
Plants  from  self- 
fertilised  Plants. 

L 

Inches. 
121 

HI 

Inches. 
81 

II. 

131 

10 

9| 
HI 

III. 

14f 
13| 

H8 
HI 

Total  in  inches. 

75-38 

61-88 

128 


ADONIS   ^RTIVALIS. 


Chap.  IV. 


derived  from  trie  crossed  plants  flowered  in  all  three  pots  before 
the  naturally  crossed  seedlings  derived  from  the  self-fertilised 
plants.  When  both  lots  were  in  full  flower,  the  two  tallest 
plants  on  each  side  of  each  pot  were  measured,  and  the  result 
is  shown  in  the  preceding  table. 

The  average  height  of  the  six  tallest  plants  derived  from  the 
crossed  plants  is  12*56  inches;  and  that  of  the  six  tallest  plants 
derived  f  rom  the  self-fertilised  plants  is  10 *  31  inches ;  or  as 
100  to  82.  We  here  see  a  considerable  difference  in  height 
between  the  two  sets,  though  very  far  from  equalling  that  in  the 
previous  trials  between  the  offspring  from  crossed  and  self- 
fertilised  flowers.  This  difference  must  be  attributed  to  the 
latter  set  of  plants  having  inherited  a  weak  constitution  from 
their  parents,  the  offspring  of  self-fertilised  flowers  ;  notwith- 
standing that  the  parents  themselves  had  been  freely  inter- 
crossed with  other  plants  by  the  aid  of  insects. 


X.  KANUNCULACE2E.— Abonis  2estivalis. 

The  results  of  my  experiments  on  this  plant  are  hardly  worth 
giving,  as  I  remark  in  my  notes  made  at  the  time,  " seedlings, 
from  some  unknown  cause,  all  miserably  unhealthy."  Nor  did  they 
ever  become  healthy ;  yet  I  feel  bound  to  give  the  present  case, 
as  it  is  opposed  to  the  general  results  at  which  I  have  arrived. 
Fifteen  flowers  were  crossed  and  all  produced  fruit,  containing 
on  an  average  32 '  5  seeds ;  nineteen  flowers  were  fertilised  with 
their  own  pollen,  and  they  likewise  all  yielded  fruit,  containing 
a  rather  larger  average  of  34*5  seeds  ;  or  as  100  to  106.  Seedlings 
were  raised  from  these  seeds.  In  one  of  the  pots  all  the  self- 
fertilised  plants  died  whilst  quite  young;  in  the  two  others,  the 
measurements  were  as  follows  : 

Table  XLIII. 
Adonis  aestivalis. 


No.  of  Pot.                 Oossed  Hants. 

Self-fertilised  Plants. 

Inches. 
I.                               14 
13| 

Inches. 
13  i 
13| 

II.               |                16| 

!           131 

151 
15 

Total  in  inches.                   57*00         i                57*25 

Chap  IV.  DELrHINIUM   CONSOLIDA.  129 

The  average  height  of  the  four  crossed  plants  is  14 '  25,  and 
that  of  the  four  self-fertilised  plants  14 "31;  or  as  100  to  100 "4; 
so  that  they  were  in  fact  of  equal  height.  According  to  Professor 
H.  Hoffmann,*  this  plant  is  proterandrous ;  nevertheless  it  yields 
plenty  of  seeds  -when  protected  from  insects. 

Delphinium  consolida. 

It  has  been  said  in  the  case  of  this  plant,  as  of  so  many 
others,  that  the  flowers  are  fertilised  in  the  bud,  and  that 
distinct  plants  or  varieties  can  never  naturally  intercross.!  But 
this  is  an  error,  as  we  may  infer,  firstly  from  the  flowers  being 
proterandrous, — the  mature  stamens  bending  up,  one  after  the 
other,  into  the  passage  which  It  ads  to  the  nectary,  and  afterwards 
the  mature  pistils  bending  in  the  same  direction;  secondly,  from 
the  number  of  humble-bees  which  visit  the  flowers  J ;  and  thirdly, 
from  the  greater  fertility  of  the  flowers  when  crossed  with  pollen 
from  a  distinct  plant  than  when  spontaneously  self -fertilised.  In 
the  year  1863  I  enclosed  a  large  branch  in  a  netj  and  crossed  five 
flowers  with  pollen  from  a  distinct  plant ;  these  yielded  capsules 
containing  on  an  average  35  •  2  very  fine  seeds,  with  a  maximum  of 
forty-two  in  one  capsule.  Thirty-two  other  flowers  on  the  same 
branch  produced  twenty-eight  spontaneously  self-fertilised  cap- 
sules, containing  on  an  average  17  *  2  seeds,  with  a  maximum  in 
one  of  thirty-six  seeds.  But  six  of  these  capsules  were  very  poor, 
yielding  only  from  one  to  five  seeds ;  if  these  are  excluded,  the 
remaining  twenty-two  capsules  give  an  average  of  20*9  seeds, 
though  many  of  these  seeds  were  small.  The  fairest  ratio, 
therefore,  for  the  number  of  seeds  produced  by  a  cross  and  by 
spontaneous  self-fertilisation  is  as  100  to  59.  These  seeds  were 
not  sown,  as  I  had  too  many  other  experiments  in  progress. 

In  the  summer  of  1867,  which  was  a  very  unfavourable  one, 
I  again  crossed  several  flowers  under  a  net  with  pollen  from  a 
distinct  plant,  and  fertilised  other  flowers  on  the  same  plant  with 
their  own  pollen.  The  former  yielded  a  much  larger  proportion 
of  capsules  than  the  latter ;  and  many  of  the  seeds  in  the  sel  f- 
fertilised  capsules,  though  numerous,  were  so  poor  that  an  equal 
number  of  seeds  from  the  crossed  and  self-fertilised  capsules 


*  '  Zur     Speciesfrage,'     1S7-5,  %  Their  structure  is  described 

p.  11.  by  H.  Miiller,  '  Befruchtung,'  &c, 

t  Decaisne,  *  Comptes-Bendus,'  p.  122, 
July,  1803,  p.  5. 


130 


VISCARIA   OCULATA. 


Chap.  IV 


were  in  weight  as  100  to  45.  The  two  lots  were  allowed  to 
germinate  on  sand,  and  pairs  were  planted  on  the  opposite  sides 
of  four  pots.  "When  nearly  two-thirds  grown  they  were 
measured,  as  shown  in  the  following  table  : — 

Table  XLIV. 
Delphinium  consolida. 


No.  of  Pot. 

Crossed  Plants. 

Self-fe:tilised  Plants. 

I. 

Inches. 
11 

Inches. 
11 

II. 

19 
16f 

16§ 

III. 

26 

22 

IV. 

Q4 

8 

81 

n 

Total  iu  inches. 

89-75 

75-50 

The  sis  crossed  plants  here  average  14-95,  and  the  six  self- 
fertilised  12  •  50  inches  in  height ;  or  as  100  to  84.  "When  fully 
grown  they  were  again  measured,  but  from  want  of  time  ODly  a 
single  plant  on  each  side  was  measured ;  so  that  I  have  thought 
it  best  to  give  the  earlier  measurements.  At  the  later  period 
the  three  tallest  crossed  plants  still  exceeded  considerably  in 
height  the  three  tallest  self- fertilised,  but  not  in  quite  so  great 
a  degree  as  before.  The  pots  were  left  uncovered  in  the  green- 
house, but  whether  the  flowers  were  intercrossed  by  bees  or  self- 
fertilised  I  do  not  know.  The  six  crossed  plants  produced  282 
mature  and  immature  capsules,  whilst  the  six  self-fertilised 
plants  produced  only  159  ;  or  as  100  to  56.  So  that  the  crossed 
plants  were  very  much  more  productive  than  the  self-fertilised. 


XL  CAKYOPHYLLACE^.— Viscakia  octjlata. 

Twrelve  flowers  were  crossed  with  pollen  from  another  plant, 
and  yielded  ten  capsules,  containing  by  weight  5 '77  grains  of 
seeds.  Eighteen  flowers  were  fertilised  with  their  own  pollen 
and  yielded  twelve  capsules,  containing  by  weight  2-63  grains. 
Therefore  the  seeds  from  an  equal  number  of  crossed  and  self- 


Chap.  IV.  VISCARIA  OCULATA.  131 

fertilised  flowers  would  have  been  in  weight  as  100  to  38.  I  had 
previously  selected  a  medium-sized  capsule  from  each  lot,  and 
counted  the  seeds  in  both ;  the  crossed  one  contained  284,  and 
the  self-fertilised  one  126  seeds ;  or  as  100  to  44.  These  seeds 
were  sown  on  opposite  sides  of  three  pots,  and  several  seedlings 
raised;  but  only  the  tallest  flower-stem  of  one  plant  on  each 
side  was  measured.  The  three  on  the  crossed  side  averaged  32  ■  5 
inches,  and  the  three  on  the  self-fertilised  side  34  inches  in 
height;  or  as  100  to  104.  But  this  trial  was  on  much  too  small 
a  scale  to  be  trusted;  the  plants  also  grew  so  unequally  that 
one  of  the  three  flower-stems  on  the  crossed  plants  was  very 
nearly  twice  as  tall  as  that  on  one  of  the  others ;  and  one  of 
the  three  flower-stems  on  the  self- fertilised  plants  exceeded  in 
an  equal  degree  one  of  the  others. 

In  the  following  year  the  experiment  was  repeated  .on  a  larger 
scale :  ten  flowers  were  crossed  on  a  new  set  of  plants  and 
yielded  ten  capsules  containing  by  weight  6 "  54  grains  of  seed. 
Eighteen  spontaneously  self-fertilised  capsules  were  gathered, 
of  which  two  contained  no  seed  ;  the  other  sixteen  contained  by 
weight  6 "  07  grains  of  seed.  Therefore  the  weight  of  seed  from 
an  equal  number  of  crossed  and  spontaneously  self-fertilised 
flowers  (instead  of  artificially  fertilised  as  in  the  previous  case) 
was  as  100  to  58. 

The  seeds  after  germinating  on  sand  were  planted  in  pairs  on 
the  opposite  sides  of  four  pots,  with  all  the  remaining  seeds  sown 
crowded  in  the  opposite  sides  of  a  fifth  pot ;  in  this  latter  pot 
only  the  tallest  plant  on  each  side  was  measured.  Until  the 
seedlings  had  grown  about  5  inches  in  height  no  difference 
could  be  perceived  in  the  two  lots.  Both  lots  flowered  at  nearly 
the  same  time.  When  they  had  almost  done  flowering,  the 
tallest  flower-stem  on  each  plant  was  measured,  as  shown  in  the 
following  table  (XLV.). 

The  fifteen  crossed  plants  here  averago  34  ■  5,  and  the  fifteen 
self-fertilised  33-55  inches  in  height;  or  as  100  to  97.  So  that 
the  excess  of  height  of  the  crossed  plants  is  quite  insignificant.  In 
productiveness,  however,  the  difference  was  much  more  plainly 
marked.  All  the  capsules  were  gathered  from  both  lots  of  plants 
(except  from  the  crowded  and  unproductive  ones  in  Pot  V.),  and 
at  the  close  of  the  season  the  few  remaining  flowers  were  added 
in.  The  fourteen  crossed  plants  produced  381,  whilst  the  four- 
teen self-fertilised  plants  produced  only  293  capsules  and  flowers; 
or  as  100  to  77. 


132 


DIANTHUS    CARYOPHYLLUS. 


Chap.  IV. 


Table  XLV. 
Viscaria  oculata. 


DlANTHTJS   CARYOPHYLLUS. 

The  common  carnation  is  strongly  proterandrous,  and  there- 
fore depends  to  a  large  extent  upon  insects  for  fertilisation.  I 
have  seen  only  humble-bees  visiting  the  flowers,  but  I  dare  say 
other  insects  likewise  do  so.  It  is  notoiious  that  if  pure  seed  is 
desired,  the  greatest  care  is  necessary  *  to  prevent  the  varieties 
which  grow  in  the  same  garden  from  intercrossing.  The  pollen 
is  generally  shed  and  lost  before  the  two  stigmas  in  the  same 
flower  diverge  and  are  ready  to  be  fertilised.  I  was  therefore 
often  forced  to  use  for  self-fertilisation  pollen  from  the  same 
plant  instead  of  from  the  same  flower.  But  on  two  occasions, 
when  I  atttnded  to  this  point,  I  was  not  able  to  detect  any 
marked  difference  in  the  numbtr  of  seeds  produced  by  these  two 
forms  of  self-fertilisation. 


« Gardeners'  Chronicle,'  1817.  p.  268. 


CHAP.  IV.    CEOSSED   AND   SELF-FEKTILISED   PLANTS.      133 

Several  single-flowered  carnations  were  planted  in  good  soil, 
and  were  all  covered  with  a  net.  Eight  flowers  were  crossed 
with  pollen  from  a  distinct  plant  and  yielded  six  capsules^ 
containing  on  an  average  88*6  seeds,  with  a  maximum  in  one  of 
112  seeds.  Eight  other  flowtrs  were  self-fertilised  in  the 
manner  above  described,  and  yielded  seven  capsules  containing 
on  an  average  82  steds,  with  a  maximum  in  one  of  112  seeds. 
So  that  there  was  very  little  difference  in  the  number  of  seeds 
produced  by  cross-fertilisation  and  self-fertilisation,  viz.,  as 
100  to  92.  As  these  plants  were  covered  by  a  net,  they  pro- 
duced spontaneously  only  a  few  capsules  containing  any  seeds, 
and  these  few  may  perhaps  be  attributed  to  the  action  of 
Thrips  and  other  minute  insects  which  haunt  the  flowers.  A 
large  majority  of  the  spontaneously  self-fertilised  capsules  pro- 
duced by  several  plants  contained  no  seeds,  or  only  a  single  one. 
Excluding  these  latter  capsules,  I  counted  the  seeds  in  eighteen 
of  the  finest  ones,  and  these  contained  on  an  average  18  seeds. 
One  of  the  plants  was  spontaneously  self- fertile  in  a  higher  degree 
than  any  of  the  others.  On  another  occasion  a  single  covered-up 
plant  produced  spontaneously  eighteen  capsules,  but  only  two  of 
these  contained  any  seed,  namely  10  and  15. 

Crossed  and  self-fertilised  Plants  of  the  First  Generation. — The 
many  seeds  obtained  from  the  above  crossed  and  artificially 
self-fertilised  flowers  were  sown  out  of  doors,  and  two  large  beds 
of  seedlings,  closely  adjoining  one  another,  thus  raised.  This 
was  the  first  plant  on  which  I  experimented,  and  I  had  not 
then  formed  any  regular  scheme  of  operation.  When  the  two 
lots  were  in  full  flower,  I  measured  roughly  a  large  number  of 
plants  but  record  only  that  the  crossed  were  on  an  average 
fully  4  inches  taller  than  the  self-feitilised.  Judging  from 
subsequent  measurements,  we  may  assume  that  the  crossed 
plants,  were  about  28  inches,  and  the  self-fertilised  about 
21  inches  in  height;  and  this  will  give  us  a  ratio  of  100  to 
86.  Out  of  a  large  number  of  plants,  four  of  the  crossed  ones 
flowered  before  any  one  of  the  self- fertilised  plants. 

Thirty  flowers  on  these  crossed  plants  of  the  first  generation 
were  again  crossed  with  pollen  from  a  distinct  plant  of  the  same 
lot,  and  yielded  twenty-nine  capsules,  containing  on  an  average 
55 '62  seeds,  with  a  maximum  in  one  of  110  seeds. 

Thirty  flowers  on  the  self-fertilised  plants  were  again  self- 
fertilised  ;  eight  of  them  with  pollen  from  the  same  flower,  and 
the  remainder  with  pollen  from  another  flower  on  the  same 


134  DIANTHUS   CARYOPHYLLUS.  Chap.  IV. 

plant ;  and  these  produced  twenty-two  capsules,  containing  on  an 
average  35  "95  seeds,  with  a  maximum  in  one  of  61  seeds.  We 
thus  see,  judging  by  the  number  of  seeds  per  capsule,  that  the 
crossed  plauts  again  crossed  were  more  productive  than  the 
self- fertilised  again  self-fertilised,  in  the  ratio  of  100  to  65. 
Both  the  crossed  and  self-fertilised  plants,  from  having  grown 
much  crowded  in  the  two  beds,  produced  less  fine  capsules  and 
fewer  seeds  than  did  their  parents. 

Crossed  and  self-fertilised  Plants  of  the  Second  Generation. — The 
crossed  and  self-fertilised  seeds  from  the  crossed  and  self-fertilised 
plants  of  the  last  generation  were  sown  on  opposite  sides  of  two 
pots ;  but  the  seedlings  were  not  thinned  enough,  so  that  both  lots 
grew  very  irregularly,  and  most  of  the  self-fertilised  plants  after 
a  time  died  from  being  smothered.  My  measurements  were, 
therefore,  very  incomplete.  From  the  first  the  crossed  seedlings 
appeared  the  finest,  and  when  they  were  on  an  average,  by  esti- 
mation, 5  inches  high,  the  self  fertilised  plants  were  only  4 
inches.  In  both  pots  the  crossed  plants  flowered  first.  The  two 
tallest  flower-stems  on  the  crossed  plants  in  the  two  pots  were 
17  and  16j  inches  in  height ;  and  the  two  tallest  flower-stems 
on  the  self-fertilised  plants  101  and  9  inches;  so  that  their 
heights  were  as  100  to  58.  But  this  ratio,  deduced  from  only 
two  pairs,  obviously  is  not  in  the  least  trustworthy,  and  would 
not  have  been  given  had  it  not  been  otherwise  supported.  I 
state  in  my  notes  that  the  crossed  plants  were  very  much  more 
luxuriant  than  their  opponents,  and  seemed  to  be  twice  as 
bulky.  This  latter  estimate  may  be  believed  from  the  ascertained 
weights  of  the  two  lots  in  the  next  generation.  Some  flowers 
on  these  crossed  plants  were  again  crossed  with  pollen  from 
another  plant  of  the  tame  lot,  and  some  floAvers  on  the  self- 
fertilised  plants  again  self-fertilised;  and  from  the  seeds  thus 
obtained  the  plants  of  the  next  generation  were  raised. 

Crossed  and  self -fertilised  Plants  of  the  Third  Generation. — The 
seeds  just  alluded  to  were  allowed  to  germinate  on  bare  sand, 
and  were  planted  in  pairs  on  the  opposite  sides  of  four  pots. 
When  the  seedlings  were  in  full  flower,  the  tallest  stem  on  each 
plant  was  measured  to  the  base  of  the  calyx.  The  measurements 
are  given  in  the  following  table  (XL VI.).  In  Pot  I.  the  crossed 
and  self-fertilised  plants  flowered  at  the  same  time ;  but  in  the 
other  three  pots  the  crossed  flowered  first.  These  latter  plants 
also  continued  flowering  much  later  in  the  autumn  than  the 
self-fertilised. 


Uhap.  IV.  CROSSED  AND   SELF-FERTILISED  PLANTS.      135 


Table  XLVL 

Dianthus  caryophyllus  {Third  Generation). 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
28| 

27 1 

Inches. 
30 
26 

II. 

29 
29| 

305 

27 1 

in. 

28| 
23  i 

31| 
24  § 

IV. 

27 
33 1 

30 
25 

Total  in  inches. 

227-13 

225-75 

The  average  height  of  the  eight  crossed  plants  is  here  28 "  39 
inches,  and  of  the  eight  self-fertilised  28  -21;  or  as  100  to  99. 
So  that  there  was  no  difference  in  height  worth  speaking  of; 
but  in  general  vigour  and  luxuriance  there  was  an  astonishing 
difference,  as  shown  by  their  weights.  After  the  seed-capsules 
had  been  gathered,  the  eight  crossed  and  the  eight  self-fertilised 
plants  were  cut  down  and  weighed;  the  former  weighed  43 
ounces,  and  the  latter  only  21  ounces ;  or  as  100  to  49. 

These  plants  were  all  kept  under  a  net,  so  that  the  capsules 
which  they  produced  must  have  been  all  spontaneously  self- 
fertilised.  The  eight  crossed  plants  produced  twenty-one  such 
capsules,  of  which  only  twelve  contained  any  seed,  averaging 
8*5  per  capsule.  On  the  other  hand,  the  eight  self-fertilised 
plants  produced  no  less  than  thirty-six  capsules,  of  which  I 
examined  twenty-five,  and,  with  the  exception  of  three,  all 
contained  seeds,  averaging  10 '  63  seeds  per  capsule.  Thus  the 
proportional  number  of  seeds  per  capsule  produced  by  the  plants 
of  crossed  origin  to  those  produced  by  the  plants  of  self-fertilised 
origin  (both  lots  being  spontaneously  self-fertilised)  was  as  100 
to  125.  This  anomalous  result  is  probably  due  to  some  of  the 
self-fertilised  plants  having  varied  so  as  to  mature  their  pollen 
and  stigmas  more  nearly  at  the  same  time  than  is  proper  to 
the  species ;  and  we  have  already  seen  that  some  plants  in  the 
7 


136  DIANTHUS  CAEYOPHYLLUS.  Chap.  IV. 

first  experiment  differed  from  the  others  in  being  slightly  more 
self-fertile. 

Tlie  Effects  of  a  Cross  with  afresh  Stock. — Twenty  flowers  on  the 
self-fertilised  plants  of  the  last  or  third  generation,  in  Table  XLVL, 
were  fertilised  with  their  own  pollen,  but  taken  from  other 
flowers  on  the  same  plants.  These  produced  fifteen  capsules, 
which  contained  (omitting  two  with  only  three  and  six  seeds) 
on  an  average  47 "  23  seeds,  with  a  maximum  of  seventy  in  one. 
The  self-fertilised  capsules  from  the  self-fertilised  plants  of  the 
first  generation  yielded  the  much  lower  average  of  35 '  95  seeds ; 
but  as  these  latter  plants  grew  extremely  crowded,  nothing  can 
be  inferred  with  respect  to  this  difference  in  their  self-fertility. 
The  seedlings  raised  from  the  above  seeds  constitute  the  plants 
of  the  fourth  self-fertilised  generation  in  the  following  table 
(XLVIL). 

Twelve  flowers  on  the  same  plants  of  the  third  self-fertilised 
generation,  in  Table  XLVL,  were  crossed  with  pollen  from  the 
crossed  plants  in  the  same  table\  These  crossed  plants  had  been 
intercrossed  for  the  three  previous  generations;  and  many  of 
them,  no  doubt,  were  more  or  less  closely  inter-related,  but  not 
so  closely  as  in  some  of  the  experiments  with  other  species ;  for 
several  carnation  plants  had  been  raised  and  crossed  in  the 
earlier  generations.  They  were  not  related,  or  only  in  a  distant 
degree,  to  the  self-fertilised  plants.  The  parents  of  both  the 
self-fertilised  and  crossed  plants  had  been  subjected  to  as  nearly 
as  possible  the  same  conditions  during  the  three  previous  genera- 
tions. The  above  twelve  flowers  produced  ten  capsules,  contain- 
ing on  an  average  48-66  seeds,  with  a  maximum  in  one  of 
seventy-two  seeds.  The  plants  raised  from  these  seeds  may  be 
called  the  intercrossed. 

Lastly,  twelve  flowers  on  the  same  self-fertilised  plants  of  the 
third  generation  were  crossed  with  pollen  from  plants  which 
had  been  raised  from  seeds  purchased  in  London.  It  is  almost 
certain  that  the  plants  which  produced  these  seeds  had  grown 
under  very  different  conditions  to  those  to  which  my  self- 
fertilised  and  crossed  plants  had  been  subjected ;  and  they  were 
in  no  degree  related.  The  above  twelve  flowers  thus  crossed 
all  produced  capsules,  but  these  contained  the  low  average  of 
37  "41  seeds  per  capsule,  with  a  maximum  in  one  of  sixty- four 
seeds.  It  is  surprising  that  this  cross  with  a  fresh  stock  did  not 
give  a  much  higher  average  number  of  seeds ;  for,  as  we  shall 
immediately  see,  the  plants  raised  from  these  seeds,  which  may 


Chap.  IV. 


CEOSS  WITH  A  FRESH  STOCK. 


137 


be  called  the  London-crossed,  benefited  greatly  by  the  cross,  both 
in  growth  and  fertility. 

The  above  three  lots  of  seeds  were  allowed  to  germinate  on 
bare  sand.  Many  of  the  London-crossed  germinated  before  the 
others,  and  were  rejected ;  and  many  of  the  intercrossed  later 
than  those  of  the  other  two  lots.  The  seeds  after  thus  germina- 
ting were  planted  in  ten  pots,  made  tripartite  by  superficial 


Table  XLVII. 
Dianthus  caryophyllus. 


138  DIANTHUS  CAEYOPHYLLUS.  Chap,  IV. 

divisions ;  but  when  only  two  kinds  of  seeds  germinated  at  the 
same  time,  they  were  planted  on  the  opposite  sides  of  other  pots ; 
and  this  is  indicated  by  blank  spaces  in  one  of  the  three  columns 
in  Table  XL VII.  An  0  in  the  table  signifies  that  the  seedling 
died  before  it  was  measured;  and  a  +  signifies  that  the  plant 
did  not  produce  a  flower-stem,  and  therefore  was  not  measured. 
It  deserves  notice  that  no  less  than  eight  out  of  the  eighteen  self- 
fertilised  plants  either  died  or  did  not  flower;  whereas  only 
three  out  of  the  eighteen  intercrossed,  and  four  out  of  the  twenty 
London-crossed  plants,  were  in  this  predicament.  The  self- 
fertilised  plants  had  a  decidedly  less  vigorous  appearance 
than  the  plants  of  the  other  two  lots,  their  leaves  being 
smaller  and  narrower.  In  only  one  pot  did  a  self-fertilised  plant 
flower  before  one  of  the  two  kinds  of  crossed  plants,  between 
which  there  was  no  marked  difference  in  the  period  of  flowering, 
The  plants  were  measured  to  the  base  of  the  calyx,  after  they 
had  completed  their  growth,  late  in  the  autumn. 

The  average  height  of  the  sixteen  London-crossed  plants  in 
the  preceding  table  is  32-82  inches;  that  of  the  fifteen  inter- 
crossed plants,  28  inches ;  and  that  of  the  ten  self-fertilised 
plants,  26  ■  55. 

So  that  in  height  we  have  the  following  ratios : — 

The  London-crossed  to  the  self- fertilised  as  100  to  81 
The  London-crossed  to  the  intercrossed  as  100  to  85 
The  intercrossed  to  the  self-fertilised  as        100  to  95 

These  three  lots  of  plants,  which  it  should  be  remembered 
were  all  derived  on  the  mother-side  from  plants  of  the  third 
self-fertilised  generation,  fertilised  in  three  different  ways,  were 
left  exposed  to  the  visits  of  insects,  and  their  flowers  were  freely 
crossed  by  them.  As  the  capsules  of  each  lot  became  ripe  they 
were  gathered  and  kept  separate,  the  empty  or  bad  ones  being 
thrown  away.  But  towards  the  middle  of  October,  when  the 
capsules  could  no  longer  ripen,  all  were  gathered  and  were 
counted,  whether  good  or  bad.  The  capsules  were  then  crushed, 
and  the  seed  cleaned  by  sieves  and  weighed.  For  the  sake  of 
uniformity  the  results  are  given  from  calculation,  as  if  there  had 
been  twenty  plants  in  each  lot. 

The  sixteen  London-crossed  plants  actually  produced  286 
capsules;  therefore  twenty  such  plants  would  have  produced 
357  •  5  capsules ;  and  from  the  actual  weight  of  the  seeds,  the 
twenty  plants  would  have  yielded  462  grains  weight  of  seeds. 


Chap.  IV.  COLOUR   OF   THE   FLOWERS.  139 

The  fifteen  intercrossed  plants  actually  produced  157  capsules ; 
therefore  twenty  of  them  would  have  produced  209  "3  capsules 
and  the  seeds  would  have  weighed  208 "  48  grains. 

The  ten  self-fertilised  plants  actually  produced  70  capsules 
therefore  twenty  of  them  would  have  produced  140  capsules ; 
and  the  seeds  would  have  weighed  153  ■  2  grains. 

From  these  data  we  get  the  following  ratios : — 

Number  of  capsules  produced  by  an  equal  number  of  plants  of 
the  three  lots. 

Number  of  Capsules 
The  London-crossed  to  the  self-fertilised,  as  100  to  39 
The  London-crossed  to  the  intercrossed,  as    100  to  45 
The  intercrossed  to  the  self-fertilised,  as        100  to  67 

Weight  of  seeds  produced  by  an  equal  number  of  plants  of  the 
three  lots. 

Weight  of  Seed. 
The  London-crossed  to  the  self- fertilised,  as  100  to  33 
The  London-crossed  to  the  intercrossed,  as   100  to  45 
The  intercrossed  to  the  self-fertilised,  as        100  to  73 

We  thus  see  how  greatly  the  offspring  from  the  self-fertilised 
plants  of  the  third  generation  crossed  by  a  fresh  stock,  had 
their  fertility  increased,  whether  tested  by  the  number  of  cap- 
sules produced  or  by  the  weight  of  the  contained  seeds ;  this 
latter  being  the  more  trustworthy  method.  Even  the  offspring 
from  the  self-fertilised  plants  crossed  by  one  of  the  crossed 
plants  of  the  same  stock,  notwithstanding  that  both  lots  had 
been  long  subjected  to  the  same  conditions,  had  their  fertility 
considerably  increased,  as  tested  by  the  same  two  methods. 

In  conclusion  it  may  be  well  to  repeat  in  reference  to  the 
fertility  of  these  three  lots  of  plants,  that  their  flowers  were 
left  freely  exposed  to  the  visits  of  insects  and  were  undoubtedly 
crossed  by  them,  as  may  be  inferred  from  the  large  number  of  good 
capsules  produced.  These  plants  were  all  the  offspring  of  the 
same  mother-plants,  and  the  strongly  marked  difference  in  their 
fertility  must  be  attributed  to  the  nature  of  the  pollen  employed 
in  fertilising  their  parents ;  and  the  difference  in  the  nature  of  the 
pollen  must  be  attributed  to  the  different  treatment  to  which 
the  pollen-bearing  parents  had  been  subjected  during  several 
previous  generations. 

Colour  of  the  Mowers. — The  flowers  produced  by  the  self-fertilised 


140 


HIBISCUS  AFRICANUS. 


Chap.  TV. 


plants  of  the  last  or  fourth  generation  were  as  uniform  in  tint 
as  those  of  a  wild  species,  being  of  a  pale  pink  or  rose  colour. 
Analogous  cases  with  Mimulus  and  Ipomcea,  after  several 
generations  of  self-fertilisation,  have  been  already  given.  The 
flowers  of  the  intercrossed  plants  of  the  fourth  generation  were 
likewise  nearly  uniform  in  colour.  On  the  other  hand,  the  flowers 
of  the  London-crossed  plants,  or  those  raised  from  a  cross  with 
the  fresh  stock  which  bore  dark  crimson  flowers,  varied  extremely 
in  colour,  as  might  have  been  expected,  and  as  is  the  general 
rule  with  seedling  carnations.  It  deserves  notice  that  only  two 
or  three  of  the  London-crossed  plants  produced  dark  crimson 
flowers  like  those  of  their  fathers,  and  only  a  very  few  of  a  pale 
pink  like  those  of  their  mothers.  The  great  majority  had  their 
petals  longitudinally  and  variously  striped  with  the  two  colours, 
— the  groundwork  tint  being,  however,  in  some  cases  darker 
than  that  of  the  mother-plants. 

XII.  MALYACE2E  —  Hibiscus  afkicanus. 

Many  flowers  on  this  Hibiscus  were  crossed  with  pollen  from 
a  distinct  plant,  and  many  others  were  self-fertilised.  A  rather 
larger  proportional  number  of  the  crossed  than  of  the  self- 
fertilised  flowers  yielded  capsules,  and  the  crossed  capsules  con- 
tained rather  more  seeds.  The  self-fertilised  seeds  were  a  little 
heavier  than  an  equal  number  of  the  crossed  seeds,  but  they 
germinated  badly,  and  I  raised  only  four  plants  of  each  lot.  In 
three  out  of  the  four  pots,  the  crossed  plants  flowered  first. 


Table  XLVIII. 
Hibiscus  qfricanus. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

L 

Inches. 
13 1 

Inches. 
16 1 

II. 

14 

14 

III. 

8 

7 

IV. 

17| 

20f 

Total  in  inches. 

53-00 

57-75 

Chap.  IV.  g     HIBISCUS  AFRICANUS.  141 

The  four  crossed  plants  average  13  •  25,  and  the  four  self-fer- 
tilised 14 *43  inches  in  height;  or  as  100  to  109.  Here  we  have 
the  unusual  case  of  self-fertilised  plants  exceeding  the  crossed 
in  height ;  but  only  four  pairs  were  measured,  and  these  did  not 
grow  well  or  equally.  I  did  not  compare  the  fertility  of  the  two 
lots. 


142  PELAKGONIUM  ZONALE.  Chap.  V 


CHAPTEE  V. 

GeEANIACE^:,  LEGTJMINOSiE,  Onageacee,  etc. 

Pelargonium  zonale,  a  cross  between  plants  propagated  by  cuttings 
does  no  good — Tropseolum  minus — Limnantbes  douglasii — Lupinus 
luteus  and  pilosus — Phaseolus  multiflorus  and  vulgaris — Lathyrus 
odoratus,  varieties  of,  never  naturally  intercross  in  England — Pisum 
sativum,  varieties  of,  rarely  intercross,  but  a  cross  between  them 
highly  beneficial — Sarothamnus  scoparius,  wonderful  effects  of  a 
cross — Ononis  minutissima,  cleistogene  flowers  of— Summary  on 
the  Leguminosse —  Clarkia  elegans — Bartonia  aurea  —  Passiflora 
gracilis — Apium  petroselinum — Scabiosa  atropurpurea — Lactuca 
sativa — Specularia  speculum — Lobelia  ramosa,  advantages  of  a 
cross  during  two  generations — Lobelia  fulgens — Nemophila  insignis, 
great  advantages  of  a  cross — Borago  officinalis — Nolana  prostrata. 

Xin.  GEKANIACE.33.— Pelargonium  zonale. 

This  plant,  as  a  general  rule,  is  strongly  proterandrous,*  and 
is  therefore  adapted  for  cross-fertilisation  by  the  aid  of  insects. 
Some  flowers  on  a  common  scarlet  variety  were  self-fertilised, 
and  other  flowers  were  crossed  with  pollen  from  another  plant; 
but  no  sooner  had  I  done  so,  than  I  remembered  that  these 
plants  had  been  propagated  by  cuttings  from  the  same  stock, 
and  were  therefore  parts  in  a  strict  sense  of  the  same  individual. 
Nevertheless,  having  made  the  cross  I  resolved  to  save  the  seeds, 
which,  after  germinating  on  sand,  were  planted  on  the  opposite 


*  Mr.  J.  Denny,  a  great  raiser  which  also  the  pistil  is  frequently 

of  new  varieties  of  pelargoniums,  short,  so  when  it  expands  it  is 

after  stating  that  this  species  is  smothered    as    it    were    by    the 

protei-androus,  adds  (' The  Florist  bursting  anthers;  these  varieties 

and  Pomologist,'  Jan.  1872,  p.  11)  are  great  feeders,  each  pip  being 

"  there  are  some  varieties,  espe-  fertilised  by  its  own  pollen.      I 

cially  those  with  petals  of  a  pink  would   instance   Christine  as  an 

colour,  or  which  possess  a  weakly  example  of  this  fact."     We  have 

constitution,  where  the  pistil  ex-  here  an  interesting  case  of  va- 

pands  as  soon  as  or  even  before  liability  in  an    important  func- 

the    pollen-bag    bursts,    and    in  tional  point. 


Chap.  V. 


PELAKGONTUM    ZONALE. 


143 


sides  of  three  pots.  In  one  pot  the  quasi-crossed  plant  was  very- 
soon  and  ever  afterwards  taller  and  finer  than  the  self-fertilised. 
In  the  two  other  pots  the  seedlings  on  both  sides  were  for  a  time 
exactly  equal ;  but  when  the  self- fertilised  plants  were  about 
10  inches  in  height,  they  surpassed  their  antagonists  by  a  little, 
and  ever  afterwards  showed  a  more  decided  and  increasing 
advantage ;  so  that  the  self-fertilised  plants,  taken  altogether, 
were  somewhat  superior  to  the  quasi-crossed  plants.  In  this 
case,  as  in  that  of  the  Origanum,  if  individuals  which  have  been 
asexually  propagated  from  the  same  stock,  and  which  have  been 
long  subjected  to  the  same  conditions,  are  crossed,  no  advantage 
whatever  is  gained. 

Several  flowers  on  another  plant  of  the  same  variety  were 
fertilised  with  pollen  from  the  younger  flowers  on  the  same  plant, 
so  as  to  avoid  using  the  old  and  long-shed  pollen  from  tbe  same 
flower,  as  I  thought  that  this  latter  might  be  less  efficient  than 
fresh  pollen.  Other  flowers  on  the  same  plant  were  crossed  with 
fresh  pollen  from  a  plant  which,  although  closely  similar,  was 
known  to  have  arisen  as  a  distinct  seedling.  The  self-fertilised 
seeds  germinated  rather  before  the  others  ;  but  as  soon  as  I  got 
equal  pairs  they  were  planted  on  the  opposite  sides  of  four  pots. 

Table  XLIX. 

Pelargonium  zonale. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
19 1 

Inches. 
25| 
12| 

II. 

15 

12§ 

19f 

22 1 

III. 

30g 
18| 

193 

IV. 

38 

98 

Total  in  inches. 

156-50 

116-38 

When  the  two  lots  of  seedlings  were  between  4  and  5  inches  in 
height  they  were  equal,  excepting  in  Pot  IV.,  in  which  the  crossed 
plant  was  much  the  tallest.  When  between  11  and  14  inches 
in  height,  they  were  measured  to  the  tips  of  their  uppermost 


144  TEOP^OLUM  MINUS.  Chap.  V. 

leaves;  the  crossed  averaged  13-46,  and  the  self-fertilised  11*07 
inches  in  height,  or  as  100  to  82.  Five  months  later  they  were 
again  measured  in  the  same  manner,  and  the  results  are  given 
in  the  preceding  table. 

The  seven  crossed  plants  now  averaged  22  ■  35,  and  the  seven 
self- fertilised  16 '  62  inches  in  height,  or  as  100  to  74.  But  from 
the  great  inequality  of  the  several  plants,  the  result  is  less  trust- 
worthy than  in  most  other  cases.  In  Pot  II.  the  two  self- 
fertilised  plants  always  had  an  advantage,  except  whilst  quite 
young  over  the  two  crossed  plants. 

As  I  wished  to  ascertain  how  these  plants  would  behave 
during  a  second  growth,  they  were  cut  down  close  to  the  ground 
whilst  growing  freely.  The  crossed  plants  now  showed  their 
superiority  in  another  way,  for  only  one  out  of  the  seven  was 
killed  by  the  operation,  whilst  three  of  the  self-fertilised  plants 
never  recovered.  There  was,  therefore,  no  use  in  keeping  any  of 
the  plants  excepting  those  in  Pots  I.  and  III. ;  and  in  the 
following  year  the  crossed  plants  in  these  two  pots  showed  during 
their  second  growth  nearly  the  same  relative  superiority  over 
the  self-fertilised  plants  as  before. 

TROP2EOLTJM  MINUS. 

The  flowers  are  proterandrous,  and  are  manifestly  adapted 
for  cross-fertilisation  by  insects,  as  shown  by  Sprengel  and 
Delpino.  Twelve  flowers  on  some  plants  growing  out  of  doors 
were  crossed  with  pollen  from  a  distinct  plant  and  produced 
eleven  capsules,  containing  altogether  twenty-four  good  seeds. 
Eighteen  flowers  were  fertilised  with  their  own  pollen  and 
produced  only  eleven  capsules,  containing  twenty-two  good 
seeds ;  so  that  a  much  larger  proportion  of  the  crossed  than  of 
the  self-fertilised  flowers  produced  capsules,  and  the  crossed 
capsules  contained  rather  more  seed  than  the  self-fertilised  in 
the  ratio  of  100  to  92.  The  seeds  from  the  self-fertilised  capsules 
were  however  the  heavier  of  the  two,  in  the  ratio  of  100  to  87. 

Seeds  in  an  equal  state  of  germination  were  planted  on  the 
opposite  sides  of  four  pots,  but  only  the  two  tallest  plants  on 
each  side  of  each  pot  were  measured  to  the  tops  of  their  stems. 
The  pots  were  placed  in  the  greenhouse,  and  the  plants  trained 
up  sticks,  so  that  they  ascended  to  an  unusual  height.  In  three 
of  the  pots  the  crossed  plants  flowered  first,  but  in  the  fourth 
at  the  same  time  with  the  self-fertilised.  When  the  seedlings 
were  between  6  and  7  inches  in  height,  the  crossed  began  to 


Ohaf.  V. 


LIMNANTHES   DOUGLASII. 


145 


show  a  slight  advantage  over  their  opponents.  When  grown  to 
a  considerable  height  the  eight  tallest  crossed  plants  averaged 
44*43,  and  the  eight  tallest  self-fertilised  plants  37 '34  inches, 
or  as  100  to  84.  When  their  growth  was  completed  they  were 
again  measured,  as  shown  in  the  following  table : — 


Table  L. 

Tropaeolum  minus. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
65 
50 

Inches. 
31 
45 

II. 

69 
35 

42 
45 

III. 

70 

59 1 

50 1 
55g 

IV. 

61j 

57 1 

37  J 
61| 

Total  in  inches. 

467-5 

368-0 

The  eight  tallest  crossed  plants  now  averaged  58  "43,  and  the 
eight  tallest  self-fertilised  plants  46  inches  in  height,  or  as  100 
to  79. 

There  was  also  a  great  difference  in  the  fertility  of  the  two 
lots  which  were  left  uncovered  in  the  greenhouse.  On  the  17th 
of  September  the  capsules  from  all  the  plants  were  gathered, 
and  the  seeds  counted.  The  crossed  plants  yielded  243,  whilst 
the  same  number  of  self-fertilised  plants  yielded  only  155  seeds, 
or  as  100  to  64. 

LlMNANTHES  DOUGLASH. 

Several  flowers  were  crossed  and  self-fertilised  in  the  usual 
manner,  but  there  was  no  marked  difference  in  the  number  of 
seeds  which  they  yielded.  A  vast  number  of  spontaneously  self- 
fertilised  capsules  were  also  produced  under  the  net.  Seedlings 
were  raised  in  five  pots  from  the  above  seeds,  and  when  the 
crossed  were  about  3  inches  in  height  they  showed  a  slight 
advantage  over  the  self-fertilised.    "When  double  this  height,  the 


146 


LIMNANTHES   DOUGLASII. 


Chap.  V 


sixteen  crossed  and  sixteen  self-fertilised  plants  were  measured 
to  the  tips  of  their  leaves;  the  former  averaged  7*3  inches,  and 
the  self-fertilised  6-07  inches  in  height,  or  as  100  to  83.  In 
all  the  pots,  excepting  IV.,  a  crossed  plant  flowered  before  any 
one  of  the  self-fertilised  plants.  The  plants,  when  fully  grown, 
were  again  measured  to  the  summits  of  their  ripe  capsules,  with 
the  following  result : — 

Table  LI. 

Limnantlies  douglasii. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 

171 
17  g 
13 

Inches. 
15  \ 
16$ 
11 

IL 

20 
22 
21 
18| 

15{j 
16  § 
17 

III. 

15| 
17f 
14 

11| 

10f 
0 

IV. 

20| 

14 
18 

13 1 

13 

12§ 

V. 

17 

18| 

14§ 

14 1 
12f 

Total  in  inches. 

279-50 

207-75 

The  sixteen  crossed  plants  now  averaged  17-46,  and  the 
fifteen  (for  one  had  died)  self-fertilised  plants  13 '  85  inches  in 
height,  or  as  100  to  79.  Mr.  Galton  considers  that  a  higher  ratio 
would  be  fairer,  viz.,  100  to  76.  He  made  a  graphical  representa- 
tion of  the  above  measurements,  and  adds  the  words  "very 
good  "  to  the  curvature  thus  formed.  Both  lots  of  plants  pro- 
duced an  abundance  of  seed-capsules,  and,  as  far  as  could  be 
judged  by  the  eye,  there  was  no  difference  in  their  fertility. 


Chap.  V.  LUPINUS  LUTEUS.  147 

XIV.  LEGUMINOS.E. 

In  this  family  I  experimented  on  the  following  six 
genera,  Lupinus,  Phaseolus,  Lathyrus,  Pisum,  Saro- 
thamnus,  and  Ononis. 

Lupinus  luteus.* 

A  few  flowers  were  crossed  with  pollen  from  a  distinct  plant, 
but  owing  to  the  unfavourable  season  only  two  crossed  seeds 
were  produced.  Nine  seeds  were  saved  from  flowers  spon- 
taneously self-fertilised  under  a  net,  on  the  same  plant  which 
yielded  the  two  crossed  seeds.  One  of  these  crossed  seeds  was 
sown  in  a  pot  with  two  self-fertilised  seeds  on  the  opposite  side ; 
the  latter  came  up  between  two  and  three  days  before  the  crossed 
seed.  The  second  crossed  seed  was  sown  in  like  manner  with 
two  self-fertilised  seeds  on  the  opposite  side ;  these  latter  also  came 
up  about  a  day  before  the  crossed  one.  In  both  pots,  therefore, 
the  crossed  seedlings  from  germinating  later,  were  at  first  com- 
pletely beaten  by  the  self-fertilised ;  nevertheless,  this  state  of 
things  was  afterwards  completely  reversed.  The  seeds  were 
sown  late  in  the  autumn,  and  the  pots,  which  were  much  too 
small,  were  kept  in  the  greenhouse.  The  plants  in  consequence 
grew  badly,  and  the  self-fertilised  suffered  most  in  both  pots. 
The  two  crossed  plants  when  in  flower  during  the  following  spring 
were  9  inches  in  height ;  one  of  the  self-fertilised  plants  was 
8,  and  the  three  others  only  3  inches  in  height,  being  thus 
mere  dwarfs.  The  two  crossed  plants  produced  thirteen  pods, 
whilst  the  four  self-fertilised  plants  produced  only  a  single 
one.  Some  other  self-fertilised  plants  which  had  been  raised 
separately  in  larger  pots  produced  several  spontaneously  self- 
fertilised  pods  under  a  net,  and  seeds  from  these  were  used  in  the 
following  experiment. 

Crossed  and  self-fertilised  Plants  of  the  Second  Generation. —  The 


*  The  structure  of  the  flowers  ('  Nature,'    1872,    p.     499)    that 

of  this  plant,  and  their  manner  of  "  there  is  a  cavity  at  the  back  and 

fertilisation,  have  been  described  base  of  the  vexillum,  in  which  I 

by  H.  Miiller,  '  Befruchtung,'  &c.  have  not  been  able  to  find  nectar. 

p.    243.      The    flowers    do    not  But   the   bees,   which  constantly 

Becrete  free  nectar,  and  bees  gen-  visit  these  flowers,  certainly  go  to 

erally  visit  them  for  their  pollen.  thi3   cavity  for  what  they  want, 

Mr.    Farrer,     however,    remarks  and  not  to  the  staminal  tube." 


148 


LUPINUS  LUTEUS. 


Chap.  V. 


spontaneously  self-fertilised  seeds  just  mentioned,  and  crossed 
seeds  obtained  by  intercrossing  the  two  crossed  plants  of  the  last 
generation,  after  germinating  on  sand,  were  planted  in  pairs  on 
the  opposite  sides  of  three  large  pots.  When  the  seedlings  were 
only  4  inches  in  height,  the  crossed  had  a  slight  advantage 
over  their  opponents.  When  grown  to  their  full  height,  every 
one  of  the  crossed  plants  exceeded  its  opponent  in  height. 
Nevertheless  the  self-fertilised  plants  in  all  three  pots  flowered 
before  the  crossed !  The  measurements  are  given  in  the 
following  table : — 

Table  LII. 

Lupinus  luteus. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
33  § 
30  j 
30 

Inches. 

24 1 
18| 
28 

II. 

29^ 
30 

26 
25 

III. 

30  i 
31 
31 1 

28 
27  § 
24  i 

Total  in  inches. 

246-25 

201-75 

The  eight  crossed  plants  here  average  30*78,  and  the  eight 
self-fertilised  25 '21  inches  in  height;  or  as  100  to  82.  These 
plants  were  left  uncovered  in  the  greenhouse  to  set  their  pods, 
but  they  produced  very  few  good  ones,  perhaps  in  part  owing  to 
few  bees  visiting  them.  The  crossed  plants  produced  nine  pods, 
containing  on  an  average  3 '4  seeds,  and  the  self-fertilised  plants 
seven  pods,  containing  on  an  average  3  seeds,  so  that  the  seeds 
from  an  equal  number  of  plants  were  as  100  to  88. 

Two  other  crossed  seedlings,  each  with  two  self-fertilised 
seedlings  on  the  opposite  sides  of  the  same  large  pot,  were 
turned  out  of  their  pots  early  in  the  season,  without  being 
disturbed,  into  open  ground  of  good  quality.  They  were  thus 
subjected  to  but  little  competition  with  one  another,  in  com- 
parison with  the  plants  in  the  above  three  pots.    In  the  autumn 


Chap.  V.  LUP1NUS  PILOSUS.  149 

the  two  crossed  plants  were  about  3  inches  taller  than  the  four 
self-fertilised  plants ;  they  looked  also  more  vigorous  and  pro- 
duced many  more  pods. 

Two  other  crossed  and  self-fertilised  seeds  of  the  same  lot, 
after  germinating  on  sand,  were  planted  on  the  opposite  sides  of 
a  large  pot,  in  which  a  Calceolaria  had  long  been  growing, 
and  were  therefore  exposed  to  unfavourable  conditions :  tho 
two  crossed  plants  ultimately  attained  a  height  of  2(H  and 
20  inches,  whilst  the  two  self-fertilised  were  only  18  and  9a 
inches  high. 

Lupinus  PILOSTJS. 

From  a  series  of  accidents  I  was  again  unfortunate  in  obtaining 
a  sufficient  number  of  crossed  seedlings ;  and  the  following 
results  would  not  be  worth  giving,  did  they  not  strictly  accord 
with  those  just  given  with  respect  to  L.  luteus.  I  raised  at  first 
only  a  single  crossed  seedling,  which  was  placed  in  competition 
with  two  self-fertilised  ones  on  the  opposite  side  of  the  same 
pot.  These  plants,  without  being  disturbed,  were  soon  after- 
wards turned  into  the  open  ground.  By  the  autumn  the  crossed 
plant  had  grown  to  so  large  a  size  that  it  almost  smothered 
the  two  self-fertilised  plants,  which  were  mere  dwarfs;  and 
the  latter  died  without  maturing  a  single  pod.  Several  self- 
fertilised  seeds  had  been  planted  at  the  same  time  separately 
in  the  open  ground ;  and  the  two  tallest  of  these  were  33  and 
32  inches,  whereas  the  one  crossed  plant  was  38  inches  in  height. 
This  latter  plant  also  produced  many  more  pods  than  did  any 
one  of  the  self-fertilised  plants,  although  growing  separately.  A 
few  flowers  on  the  one  crossed  plant  were  crossed  with  pollen 
from  one  of  the  self-fertilised  plants,  for  I  had  no  other  crossed 
plant  from  which  to  obtain  pollen.  One  of  the  self-fertilised 
plants  having  been  covered  by  a  net  produced  plenty  of  spon- 
taneously self-fertilised  pods. 

Grossed  and  self -fertilised  Plants  of  the  Second  Generation. — From 
crossed  and  self-fertilised  seeds  obtained  in  the  manner  just 
described,  I  succeeded  in  raising  to  maturity  only  a  pair  of 
plants,  which  were  kept  in  a  pot  in  the  greenhouse.  The  crossed 
plant  grew  to  a  height  of  33  inches,  and  the  self-fertilised  to 
that  of  26  s  inches.  The  former  produced,  whilst  still  kept  in 
the  greenhouse,  eight  pods,  containing  on  an  average  2  "77  seeds; 
and  the  latter  only  two  pods,  containing  on  an  average  2" 5 
seeds.    The  average  height  of  the  two  crossed  plants  of  the  two 


150 


PHASEOLUS   MULTIFLORUS. 


Chap.  V. 


generations  taken  together  was  35*5,  and  that  of  the  three  self- 
fertilised  plants  of  the  same  two  generations  30 '  5 ;  or  as  100 
to  86.* 

PHASEOLUS   MULTIFLOEXrS. 

This  plant,  the  scarlet-runner  of  English  gardeners  and  the  P. 
coccineus  of  Lamarck,  originally  came  from  Mexico,  as  I  am  in- 
formed by  Mr.  Bentham.  The  flowers  are  so  constructed  that 
hive  and  humble-bees,  which  visit  them  incessantly,  almost  always 
alight  on  the  left  wing-petal,  as  tbey  can  best  suck  the  nectar 
from  this  side.  Their  weight  and  movements  depress  the  petal, 
and  this  causes  the  stigma  to  protrude  from  the  spirally- wound 
keel,  and  a  brush  of  hairs  round  the  stigma  pushes  out  the  pollen 
before  it.  The  pollen  adheres  to  the  head  or  proboscis  of  the 
bee  which  is  at  work,  and  is  thus  placed  either  on  the  stigma 
of  the  same  flower,  or  is  carried  to  another  flower,  t  Several 
years  ago  I  covered  some  plants  under  a  large  net,  and  these 
produced  on  one  occasion  about  one-third,  and  on  another  occa- 
sion about  one-eighth,  of  the  number  of  pods  which  the  same 
number  of  uncovered  plants  growing  close  alongside  produced.J 
This  lessened  fertility  was  not  caused  by  any  injury  from  the 
net,  as  I  moved  the  wing-petals  of  several  protected  flowers,  in 
the  same  manner  as  bees  do,  and  these  produced  remarkably 


*  "We  here  see  that  both  Lupi- 
nus  luteus  and  pilosus  seed  freely 
when  insects  are  excluded ;  but 
Mr.  Swale,  of  Christchurch,  in 
New  Zealand,  informs  me  (see 
'  Gardeners'  Chronicle/  1858,  p. 
828)  that  the  garden  varieties  of 
the  lupine  are  not  there  visited  by 
any  bees,  and  that  they  seed  less 
freely  than  any  other  introduced 
leguminous  plant,  with  the  excep- 
tion of  red  clover.  He  adds,  "  I 
have,  for  amusement,  during  the 
summer,  released  the  stamens  with 
a  pin,  and  a  pod  of  seed  has  always 
rewarded  me  for  my  trouble,  the 
adjoining  flowers  not  so  served 
having  all  proved  blind."  I  do 
not  know  to  what  species  this 
statement  refers. 

t  The  flowers  have  been  de- 
scribed by  Delpino,  and  in  an 
admirable  manner  by  Mr.  Farrer 


in  the  'Annals  and  Mag.  of  Nat. 
Hist.'  vol.  ii.  (4th  series)  Oct. 
1868,  p.  256.  My  son  Francis 
has  explained  ('Nature,'  Jan.  8, 
1874,  p.  189)  the  use  of  one  pecu- 
liarity in  their  structure,  namely, 
a  little  vertical  projection  on  the 
single  free  stamen  near  its  base, 
which  seems  placed  as  if  to  guard 
the  entrance  into  the  two  nectar- 
holes  in  the  staminal  sheath. 
He  shows  that  this  projection  pre- 
vents the  bees  reaching  the  nectar, 
unless  they  go  to  the  left  side  of 
the  flower,  and  it  is  absolutely 
necessary  for  cross-fertilisation 
that  they  should  alight  on  the 
left  wing-petal. 

%  '  Gardeners'  Chronicle,'  1857, 
p.  725,  and  more  especially  ibid, 
1858,  p.  828.  Also  'Annals  and 
Mag.  of  Nat.  Hist.'  3rd  series, 
vol.'  ii.  1858,  p.  462. 


Chap.  V.  PHASEOLUS   MULTIFLORUS.  151 

fine  pods.  When  the  net  was  taken  off,  the  flowers  were  imme- 
diately visited  by  bees,  and  it  was  interesting  to  observe  how 
quickly  the  plants  became  covered  with  young  pods.  As  the 
flowers  are  much  frequented  by  Thrips,  the  self-fertilisation  of 
most  of  the  flowers  under  the  net  may  have  been  due  to  the  action 
of  these  minute  insects.  Dr.  Ogle  likewise  covered  up  a  large 
portion  of  a  plant,  and  "  out  of  a  vast  number  of  blossoms  thus 
protected  not  a  single  one  produced  a  pod,  while  the  unprotected 
blossoms  were  for  the  most  part  fruitful."  Mr.  Belt  gives  a 
more  curious  case ;  this  plant  grows  well  and  flowers  in  Nicaragua ; 
but  as  none  of  the  native  bees  visit  the  flowers,  not  a  single  pod 
is  ever  produced.* 

From  the  facts  now  given  we  may  feel  nearly  sure  that 
individuals  of  the  same  variety  or  of  different  varieties,  if  growing 
near  each  other  and  in  flower  at  the  same  time,  would  inter- 
cross; but  I  cannot  myself  advance  any  direct  evidence  of  such 
an  occurrence,  as  only  a  single  variety  is  commonly  cultivated  in 
England.  I  have,  however,  received  an  account  from  the  Eev. 
W.  A.  Leighton,  that  plants  raised  by  him  from  ordinary  seed 
produced  seeds  differing  in  an  extraordinary  manner  in  colour 
and  shape,  leading  to  the  belief  that  their  parents  must  have 
been  crossed.  In  France  M.  Fermond  more  than  once  planted 
close  together  varieties  which  ordinarily  come  true  and  which 
bear  differently  coloured  flowers  and  seeds ;  and  the  offspring 
thus  raised  varied  so  greatly  that  there  could  hardly  be  a  doubt 
that  they  had  intercrossed.!  On  the  other  hand,  Professor  H. 
Hoffmann  %  does  not  believe  in  the  natural  crossing  of  ihe 
varieties;  for  although  seedlings  raised  from  two  varieties  growLdg 
close  together  produced  plants  which  yielded  seeds  of  a  mixed 
character,  he  found  that  this  likewise  occurred  with  plants  sepa- 
rated by  a  space  of  from  40  to  1G0  paces  from  any  other  variety ; 
he  therefore  attributes  the  mixed  character  of  the  seed  to  sponta- 


*  Dr.  Ogle,  '  Pop.  Science  Ee-  proper  manner, 

view,'    1S70,  p.    168.     Mr.  Belt,  f  '  Fecondation  chez  les  Vege- 

'The   Naturalist   in    Nicaragua,'  taux,'  185'J,  pp.  34-40.     He  adds 

1874,  p.  70.      The  latter  author  that  M.  Villiers  has  described  a 

gives     a    case    (,'  Nature,'    1S75,  spontaneous     hybrid,    which    he 

p.  26)  of  a  late  crop  of  P.  multi-  calls  P.  coccineus  hybridus,  in  the 

florus   near  London,  which  "  was  '  Annales  de  la  Sou.  K.  de  Horti- 

rendered  barren"  by  the  humble-  culture,'  June  1844. 

bees    cutting,  as  they  frequently  J  '  Bestimmung    des    Werthes 

do,  holes  at  the  bases  of  the  flowers  von  Species  und  Varietat,'  1869, 

instead  of  entering  them  in  the  pp.  47-72. 


152 


PHASEOLUS   MULTIFLOKUS. 


Chap.  V. 


neous  variability.  But  the  above  distance  would  be  very  far  from 
sufficient  to  prevent  intercrossing :  cabbages  have  been  known  to 
cross  at  several  times  this  distance ;  and  the  careful  Gartner* 
gives  many  instances  of  plants  growing  at  from  600  to  800  j  ards 
apart  fertilising  one  another.  Professor  Hoffmann  even  maintains 
that  the  flowers  of  the  kidney-bean  are  specially  adapted  for 
self-fertilisation.  He  enclosed  several  flowers  in  bags ;  and  as 
the  buds  often  dropped  off,  he  attributes  the  partial  sterility  of 
these  flowers  to  the  injurious  effects  of  the  bags,  and  not  to  the 
exclusion  of  insects.  But  the  only  safe  method  of  experimenting 
is  to  cover  up  a  whole  plant,  which  then  never  suffers. 

Self-fertilised  seeds  were  obtained  by  moving  up  and  down  in 
the  same  manner  as  bees  do  the  wing-petals  of  flowers  protected 
by  a  net ;  and  crossed  seeds  were  obtained  by  crossing  two  of  the 
plants  under  the  same  net.  The  seeds  after  germinating  on  sand 
were  planted  on  the  opposite  sides  of  two  large  pots,  and  equal- 
sized  sticks  were  given  them  to  twine  up.  When  8  inches 
in  height,  the  plants  on  the  two  sides  were  equal.  The  crossed 
plants  flowered  before  the  self-fertilised  in  both  pots.  As  soon 
as  one  of  each  pair  had  grown  to  the  summit  of  its  stick  both 
were  measured. 

Table  Lin. 
Phaseolus  multiflorus. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
87 
88 
82 1 

Inches. 
84 1 
87 
76 

II. 

90 
82| 

76 1 
87 1 

Total  in  inches. 

430-00 

411-75 

The  average  height  of  the  five  crossed  plants  is  86  inches,  and 
that  of  the  five  self-fertilised  plants  82  '35 ;  or  as  100  to  96.  The 
pots  were  kept  in  the  greenhouse,  and  there  was  little  or  no 
difference  in  the  fertility  of  the  two  lots.  Therefore  as  far  as 
these  few  observations  serve,  the  advantage  gained  by  a  cross  is 
very  small.  

*  *  Kenntniss  der  Befruchtung,'  1844,  pp.  573,  577. 


Chap.  V  LATHYKUS   ODORATUS.  153 

Phaseolus  vulgaris. 

With  respect  to  this  species,  I  merely  ascertained  that  the 
flowers  were  highly  fertile  when  insects  were  excluded,  as  indeed 
must  be  the  case,  for  the  plants  are  often  forced  during  the 
winter  when  no  insects  are  present.  Some  plants  of  two  varieties 
(viz.,  Canterbury  and  Fulrner's  Forcing  Bean)  were  covered  with 
a  net,  and  they  seemed  to  produce  as  many  pods,  containing  as 
many  beans,  as  some  uncovered  plants  growing  alongside ;  but 
neither  the  pods  nor  the  beans  were  actually  counted.  This 
difference  in  self-fertility  between  P.  vulgaris  and  rmiltiflorus  is 
remarkable,  as  these  two  species  are  so  closely  related  that 
Linnaeus  thought  that  they  formed  one.  When  the  varieties  of  P. 
vulgaris  grow  near  one  another  in  the  open  ground,  they  some- 
times cross  largely,  notwithstanding  their  capacity  for  self- 
fertilisation.  Mr.  Coe  has  given  me  a  remarkable  instance  of 
this  fact  with  respect  to  the  negro  and  a  white-seeded  and 
a  brown-seeded  variety,  which  were  all  grown  together.  The 
diversity  of  character  in  the  seedlings  of  the  second  generation 
raised  by  me  from  his  plants  was  wonderful.  I  could  add  other 
analogous  cases,  and  the  fact  is  well  known  to  gardeners.* 

LaTHTRUS   ODORATUS. 

Almost  everyone  who  has  studied  the  structure  of  papi- 
lionaceous flowers  has  been  convinced  that  they  are  specially 
adapted  for  cross-fertilisation,  although  many  of  the  species  are 
likewise  capable  of  self-fertilisation.  The  case  therefore  of 
Lathyrus  odoratus  or  the  sweet-pea  is  curious,  for  in  this 
country  it  seems  invariably  to  fertilise  itself.  I  conclude  that 
this  is  so,  as  five  varieties,  differing  greatly  in  the  colour  of  their 
flowers  but  in  no  other  respect,  are  commonly  sold  and  come 
true ;  yet  on  inquiry  from  two  great  raisers  of  seed  for  sale,  I 
find  that  they  take  no  precautions  to  insure  purity — the  five 
varieties  being  habitually  grown  close  together.f  I  have  myself 
purposely  made  similar  trials  with  the  same  result.  Although 
the  varieties  always  come  true,  yet,  as  we  shall  presently  see,  one 


*  I  have  given  Mr.  Coe's  case  ture,'  1872,  p.  242,  to  the  game 

in    the    '  Gardeners'    Chronicle,'  effect.      He  once,   however,   saw 

1858,  p.  829.    See  also  for  another  bees  visiting  the  flowers,  and  sup- 

tase,  ibid.  p.  845.  posed  that  on  tliis  occasion  they 

t  See  Mr.  W.  Earley  in  '  Na-  would  have  been  intercrossed. 


154  LATHYEUS  ODOKATUS.         Chap.  Y. 

of  the  five  well-known  varieties  occasionally  gives  birth  to  another, 
which  exhibits  all  its  usual  characters.  Owing  to  this  curiotis 
fact,  and  to  the  darker-coloured  varieties  being  the  most  pro- 
ductive, these  increase,  to  the  exclusion  of  the  others,  as  I  was 
informed  by  the  late  Mr.  Masters,  if  there  be  no  selection. 

In  order  to  ascertain  what  would  be  the  effect  of  crossing  two 
varieties,  some  flowers  on  the  Purple  sweet-pea,  which  has  a 
dark  reddish-purple  standard-petal  with  violet-coloured  wing- 
petals  and  keel,  were  castrated  whilst  very  young,  and  were 
fertilised  with  pollen  of  the  Painted  Lady.  This  latter  variety 
has  a  pale  cherry-coloured  standard,  with  almost  white  wings 
and  keel.  On  two  occasions  I  raised  from  a  flower  thus  crossed 
plants  perfectly  resembling  both  parent-forms ;  but  the  greater 
number  resembled  the  paternal  variety.  So  perfect  was  the 
resemblance,  that  I  should  have  suspected  some  mistake  in  the 
label,  had  not  the  plants,  which  were  at  first  identical  in  appear- 
ance with  the  father  or  Painted  Lady,  later  in  the  season  produced 
flowers  blotched  and  streaked  with  dark  purple.  This  is  an  in- 
teresting example  of  partial  reversion  in  the  same  individual 
plant  as  it  grows  older.  The  purple-flowered  plants  were  thrown 
away,  as  they  might  possibly  have  been  the  product  of  the 
accidental  self-fertilisation  of  the  mother-plant,  owing  to  tho 
castration  not  having  been  effectual.  But  the  plants  which 
resembled  in  the  colour  of  their  flowers  the  paternal  variety  or 
Painted  Lady  were  preserved,  and  their  seeds  saved.  Next 
summer  many  plants  were  raised  from  these  seeds,  and  they 
generally  resembled  their  grandfather  the  Painted  Lady,  but 
most  of  them  had  their  wing-petals  streaked  and  stained  with 
dark  pink ;  and  a  few  had  pale  purple  wings  with  the  standard 
of  a  darker  crimson  than  is  natural  to  the  Painted  Lady,  so 
that  they  formed  a  new  sub-variety.  Amongst  these  plants 
a  single  one  appeared  having  purple  flowers  Like  those  of  the 
grandmother,  but  with  the  petals  slightly  streaked  with  a  paler 
tint :  this  was  thrown  away.  Seeds  were  again  saved  from  the 
foregoing  plants,  and  the  seedlings  thus  raised  still  resembled 
the  Painted  Lady,  or  great-grandfather;  but  they  now  varied 
much,  the  standard  petal  varying  from  pale  to  dark  red,  in  a 
few  instances  with  blotches  of  white ;  and  the  wing-petals  varied 
from  nearly  white  to  purple,  the  keel  being  in  all  nearly  white. 

As  no  variability  of  this  kind  can  be  detected  in  plants  raised 
from  seeds,  the  parents  of  which  have  grown  during  many  suc- 
cessive generations  in  close  proximity,  we  may  infer  that  they 


Chap.  V.  LATHTEUS   ODOEATUS.  155 

cannot  have  intercrossed.  What  does  occasionally  occur  is  that 
in  a  row  of  plants  raised  from  seeds  of  one  variety,  another 
variety  true  of  its  kind  appears ;  for  instance,  in  a  long  row  of 
Scarlets  (the  seeds  of  which  had  been  carefully  gathered  from 
Scarlets  for  the  sake  of  this  experiment)  two  Pnrples  and  one 
Painted  Lady  appeared.  Seeds  from  these  three  aberrant  plants 
were  saved  and  sown  in  separate  beds.  The  seedlings  from  both 
the  Purples  were  chiefly  Purples,  but  with  some  Painted  Ladies 
and  some  Scarlets.  The  seedlings  from  the  aberrant  Painted 
Lady  were  chiefly  Painted  Ladies  with  some  Scarlets.  Each 
variety,  whatever  its  parentage  may  have  been,  retained  all  its 
characters  perfect,  and  there  was  no  streaking  or  blotching  of 
the  colours,  as  in  the  foregoing  plants  of  crossed  origin.  Another 
variety,  however,  is  often  sold,  which  is  striped  and  blotched 
with  dark  purple ;  and  this  is  probably  of  crossed  origin,  for  I 
found,  as  well  as  Mr.  Masters,  that  it  did  not  transmit  its 
characters  at  all  truly. 

From  the  evidence  now  given,  wc  may  conclude  that  the 
varieties  of  the  sweet-pea  rarely  or  never  intercross  in  this 
country ;  and  this  is  a  highly  remarkable  fact,  considering,  firstly, 
the  general  structure  of  the  flowers ;  secondly,  the  large  quantity 
of  pollen  produced,  far  more  than  is  requisite  for  self-fertilisation ; 
and  thirdly,  the  occasional  visits  of  insects.  That  insects  should 
sometimes  fail  to  cross-fertilise  the  flowers  is  intelligible,  for  I 
have  thrice  seen  humble-bees  of  two  kinds,  as  well  as  hive-bees, 
sucking  the  nectar,  and  they  did  not  depress  the  keel-petals  so 
as  to  expose  the  anthers  and  stigma ;  they  were  therefore  quite 
inefficient  for  fertilising  the  flowers.  One  of  these  bees,  namely, 
Bombus  lapidarias,  stood  on  one  side  at  the  base  of  the  standard 
and  inserted  its  proboscis  beneath  the  single  separate  stamen,  as 
I  afterwards  ascertained  by  opening  the  flower  and  finding  this 
stamen  prised  up.  Bees  are  forced  to  act  in  this  manner  from 
the  slit  in  the  staminal  tube  being  closely  covered  by  the  broad 
membranous  margin  of  the  single  stamen,  and  from  the  tube 
not  being  perforated  by  nectar-passages.  On  the  other  hand, 
in  the  three  British  species  of  Lathyrus  which  I  have  examined, 
and  in  the  allied  genus  Vicia,  two  nectar-passages  are  present. 
Therefore  British  bees  might  well  be  puzzled  how  to  act  in 
the  case  of  the  sweet-pea.  I  may  add  that  the  staminal  tube 
of  another  exotic  species,  Lathyrus  grandiflorus,  is  not  per- 
forated by  nectar-passages,  and  this  species  has  rarely  set  any 
pods  in  my  garden,  unless  the  wing-petals  were  moved  up  and 


156  LATHYRUS  ODORATUS.  Chap.  V 

down,  in  the  same  manner  as  bees  ought  to  do ;  and  then  pods 
were  generally  formed,  but  from  some  cause  often  dropped  off 
afterwards.  One  of  my  sons  caught  an  elephant  sphinx-moth 
whilst  visiting  the  flowers  of  the  sweet-pea,  but  this  insect  would 
not  depress  the  wing-petals  and  keel.  On  the  other  hand,  I  have 
seen  on  one  occasion  hive-bees,  and  two  or  three  occasions  the 
Megachile  wilhighbieUa  in  the  act  of  depressing  the  keel ;  and 
these  bees  had  the  under  sides  of  their  bodies  thickly  covered 
with  pollen,  and  could  not  thus  fail  to  carry  pollen  from  one 
flower  to  the  stigma  of  another.  Why  then  do  not  the  varieties 
occasionally  intercross,  though  this  would  not  often  happen,  as 
insects  so  rarely  act  in  an  efficient  manner  ?  The  fact  cannot,  as 
it  appears,  be  explained  by  the  flowers  being  self-fertilised  at  a 
very  early  age ;  for  although  nectar  is  sometimes  secreted  and 
pollen  adheres  to  the  viscid  stigma  before  the  flowers  are  fully 
expanded,  yet  in  five  young  flowers  which  were  examined 
by  me  the  pollen-tubes  were  not  exserted.  Whatever  the  cause 
may  be,  we  may  conclude,  that  in  England  the  varieties  never  or 
very  rarely  intercross.  But  it  does  not  follow  from  this,  that 
they  would  not  be  crossed  by  the  aid  of  other  and  larger  insects 
in  their  native  country,  which  in  botanical  works  is  said  to  be 
the  south  of  Europe  and  the  East  Indies.  Accordingly  I  wrote 
to  Professor  Delpino,  in  Florence,  and  he  informs  me  "  that  it  is 
the  fixed  opinion  of  gardeners  there  that  the  varieties  do  inter- 
cross, and  that  they  cannot  be  preserved  pure  unless  they  are 
sown  separately." 

It  follows  also  from  the  foregoing  facts  that  the  several  varieties 
of  the  sweet-pea  must  have  propagated  themselves  in  England 
by  self-fertilisation  for  very  many  generations,  since  the  time 
when  each  new  variety  first  appeared.  From  the  analogy  of  the 
plants  of  Mimulus  and  Ipomcea,  which  had  been  self-fertilised 
for  several  generations,  and  from  trials  previously  made  with 
the  common  pea,  which  is  in  nearly  the  same  state  as  the  sweet- 
pea,  it  appeared  to  me  very  improbable  that  a  cross  between  the 
individuals  of  the  same  variety  would  benefit  the  offspring.  A 
cross  of  this  kind  was  therefore  not  tried,  which  I  now  regret. 
But  some  flowers  of  the  Painted  Lady,  castrated  at  an  early 
age,  were  fertilised  with  pollen  from  the  Purple  sweet-pea ;  and 
it  should  be  remembered  that  these  varieties  differ  in  nothing 
except  in  the  colour  of  their  flowers.  The  cross  was  manifestly 
effectual  (though  only  two  seeds  were  obtained),  as  was  shown 
by  the  two  seedlings,  when  they  flowered,  closely  resembling 


Chap.  V. 


LATHYKUS  ODOKATUS. 


157 


their  father,  the  Purple  pea,  excepting  that  they  were  a  little 
lighter  coloured,  with  their  keels  slightly  streaked  with  pale 
purple.  Seeds  from  flowers  spontaneously  self-fertilised  under  a 
net  were  at  the  same  time  saved  from  the  same  mother-plant,  the 
Painted  Lady.  These  seeds  unfortunately  did  not;  germinate  on 
sand  at  the  same  time  with  the  crossed  seeds,  so  that  they  could 
not  be  planted  simultaneously.  One  of  the  two  crossed  seeds  in 
a  state  of  germination  was  planted  in  a  pot  (No.  I.)  in  which  a 
self-fertilised  seed  in  the  same  state  had  been  planted  four  days 
before,  so  that  this  latter  seedling  had  a  great  advantage  over 
the  crossed  one.  In  Pot  II.  the  other  crossed  seed  was  planted 
two  dajs  before  a  self-fertilised  one;  so  that  here  the  crossed 
seedling  had  a  considerable  advantage  over  the  self-fertilised  one. 
But  this  crossed  seedling  had  its  summit  gnawed  off  by  a  slug, 
and  was  in  consequence  for  a  time  quite  beaten  by  the  self- 
fertilised  plant.  Nevertheless  I  allowed  it  to  remain,  and  so 
great  was  its  constitutional  vigour  that  it  ultimately  beat  its  un- 
injured self-fertilised  rival.  When  all  four  plants  were  almost 
fully  grown  they  were  measured,  as  here  shown : — 


Table  LIV. 
Lathyrus  odoratus. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
80 

Inches. 
64j 

II. 

78| 

63 

Total  in  inches. 

158-5 

127-5 

The  two  crossed  plants  here  average  79  ■  25,  and  the  two  self- 
fertilised  63-75  inches  in  height,  or  as  100  to  80.  Six  flowers  on 
these  two  crossed  plants  were  reciprocally  crossed  with  pollen 
from  the  other  plant,  and  the  six  pods  thus  produced  contained 
on  an  average  six  peas,  with  a  maximum  in  one  of  seven.  Eigh- 
teen spontaneously  self-fertilised  pods  from  the  Painted  Lady, 
which,  as  already  stated,  had  no  doubt  been  self-fertilised  for 
many  previous  generations,  contained  on  an  average  only  3  ■  93 
peas,  with  a  maximum  in  one  of  five  peas ;  so  that  the  number 
of  peas  in  the  crossed  and  self-fertilised  pods  was  as  100  to  65. 


158 


LATHYEUS   ODOKATUS. 


Chap.  V. 


The  self-fertilised  peas  were,  however,  quite  as  heavy  as  those 
from  the  crossed  pods.  From  these  two  lots  of  seeds,  the  plants 
of  the  next  generation  were  raised. 

Plants  of  the  Second  Generation. — Many  of  the  self-fertilised 
peas  just  referred  to  germinated  on  sand  before  any  of  the 
crossed  ones,  and  were  rejected.  As  soon  as  I  got  equal  pairs, 
they  were  planted  on  the  opposite  sides  of  two  large  pots,  which 
were  kept  in  the  greenhouse.  The  seedlings  thus  raised  were  the 
grandchildren  of  the  Painted  Lady,  which  was  first  crossed  by 
the  Purple  variety.  When  the  two  lots  were  from  4  to  6  inches 
in  height  there  was  no  difference  between  them.  Nor  was  there 
any  marked  difference  in  the  period  of  their  flowering.  When 
fully  grown  they  were  measured,  as  follows  : — 

Table  LV. 

Lathyrus  odoratus  (Second  Generation). 


No.  of  Pot. 

Seedlings  from  Plants 

crossed  during  the 
two  previous  Genera- 
tions. 

Seedlings  from  Plants 

self-fertilised  during 

many  previous 

Generations. 

1. 

Inches. 
72j 

71 
52  § 

Inches. 
57* 
67 
56 1 

II. 

81  i 

45 1 
55 

66§ 
383 
46 

Total  in  inches. 

377-50 

331-86 

The  average  height  of  the  six  crossed  plants  is  here  62  ■  91,  and 
that  of  the  six  self-fertilised  55 "  31  inches ;  or  as  100  to  88.  There 
was  not  much  difference  in  the  fertility  of  the  two  lots ;  the 
crossed  plants  having  produced  in  the  greenhouse  thirty-five 
pois,  and  the  self-fertilised  thirty-two  pods. 

Seeds  were  saved  from  the  self-fertilised  flowers  on  these  two 
lots  of  plants,  for  the  sake  of  ascertaining  whether  the  seedlings 
thus  raised  would  inherit  any  difference  in  growth  or  vigour. 
It  must  therefore  be  understood  that  both  lots  in  the  following 
trial  are  plants  of  self-fertilised  parentage ;  but  that  in  the  one 
lot  the  plants  were  the  children  of  plants  which  had  been  crossed 
during  two  previous  generations,  having  been  before  that  self- 


Chap.  V. 


LATHYRUS    ODORATUS. 


159 


fertilised  for  many  generations ;  and  that  in  the  other  lot  they 
were  the  children  of  plants  which  had  not  been  crossed  for  very 
many  previous  generations.  The  seeds  germinated  on  sand  and 
were  planted  in  pairs  on  the  opposite  sides  of  four  pots.  They 
were  measured,  when  fully  grown,  with  the  following  result  •-  -• 

Table  LYI. 

Lathyrus  odoratus. 


No.  of  Pot. 

Self-fertilised  Plants 
from  Crossed  Plants. 

Self-fertilised  Plants 

from  Self-fertilised 

Plants. 

I. 

Inches. 

72 
72 

Inches. 
65 
611 

u. 

58 
68 
72  g 

64 
68§ 

56 1 

III. 

81    • 

60| 

IV. 

77 1 

76| 

Total  in  inches. 

501 

452 

The  average  height  of  the  seven  self-fertilised  plants,  the  off- 
spring of  crossed  plants,  is  71 "  57,  and  that  of  the  seven  self-fer- 
tilised plants,  the  offspring  of  self-fertilised  plants,  is  64  "57  ;  or 
as  100  to  90.  The  self-fertilised  plants  from  the  self-fertilised 
produced  rather  more  pods — viz.,  thirty-six — than  the  self-fer- 
tilised plants  from  the  crossed,  for  these  produced  only  thirty-one 
pods. 

A  few  seeds  of  the  same  two  lots  were  sown  in  the  opposite 
corners  of  a  large  box  in  which  a  Brugmansia  had  long  been 
growing,  and  in  which  the  soil  was  so  exhausted  that  seeds  of 
Ipomcea  purpurea  would  hardly  vegetate ;  yet  the  two  plants  of 
the  sweet-pea  which  were  raised  flourished  well.  For  a  long 
time  the  self-fertilised  plant  from  the  self-fertilised  beat  the  self- 
fertilised  plant  from  the  crossed  plant ;  the  former  flowered  first, 
and  was  at  one  time  77 2  inches,  whilst  the  latter  was  only  68z  in 
height ;  but  ultimately  the  plant  from  the  previous  cross  showed 
its  superiority  and  attained  a  height  of  108  2  inches,  whilst  the 
other  was  only  95  inches.    I  also  sowed  some  of  the  same  two 


160  PISUM  SATIVUM.  Chap.  V. 

lots  of  seeds  in  poor  soil  in  a  shady  place  in  a  shrubbery.  Here 
again  the  self-fertilised  plants  from  the  self-fertilised  for  a  long 
time  exceeded  considerably  in  height  those  from  the  previously 
crossed  plants ;  and  this  may  probably  be  attributed,  in  the 
present  as  in  the  last  case,  to  these  seeds  having  germinated 
rather  sooner  than  those  from  the  crossed  plants ;  but  at  the 
close  of  the  season  the  tallest  of  the  self-fertilised  plants  from 
the  crossed  plants  was  30  inches,  whilst  the  tallest  of  the  self- 
fertilised  from  the  self-fertilised  was  29f  inches  in  height. 

From  the  various  facts  now  given  we  see  that  plants  derived 
from  a  cross  between  two  varieties  of  the  sweet-pea,  which  differ 
in  no  respect  except  in  the  colour  of  their  flowers,  exceed 
considerably  in  height  the  offspring  from  self-fertilised  plants, 
both  in  the  first  and  second  generations.  The  crossed  plants 
also  transmit  their  superiority  in  height  and  vigour  to  their 
self-fertilised  offspring. 

Pisum  SATIVUM. 

The  common  pea  is  perfectly  fertile  when  its  flowers  are  pro- 
tected from  the  visits  of  insects;  I  ascertained  this  with  two  or 
three  different  varieties,  as  did  Dr.  Ogle  with  another.  But  the 
flowers  are  likewise  adapted  for  cross-fertilisation;  Mr.  Farrer 
specifies  *  the  following  points,  namely  :  "  The  open  blossom  dis- 
playing itself  in  the  most  attractive  and  convenient  position  for 
insects ;  the  conspicuous  vexillum ;  the  wings  forming  an  alight- 
ing place;  the  attachment  of  the  wings  to  the  keel,  by  which 
any  body  pressing  on  the  former  must  press  down  the  latter ; 
the  staminal  tube  enclosing  nectar,  and  affording  by  means  of  its 
partially  free  stamen  with  apertures  on  each  side  of  its  base  an 
open  passage  to  an  insect  seeking  the  nectar;  the  moist  and 
sticky  pollen  placed  just  where  it  will  be  swept  out  of  the  apex 
of  the  keel  against  the  entering  insect ;  the  stiff  elastic  style  so 
placed  that  on  a  pressure  being  applied  to  the  keel  it  will  be 
pushed  upwards  out  of  the  keel ;  the  hairs  on  the  style  placed 
on  that  side  of  the  style  only  on  which  there  is  space  for  the 
pollen,  and  in  such  a  direction  as  to  sweep  it  out;  and  the 
stigma  so  placed  as  to  meet  an  entering  insect, —  all  these 
become  correlated  parts  of  one  elaborate  mechanism,  if   we 


*  'Nature,'   Oct.  10,   1872,   p.       description   of  the  flowera,  '  Be- 
479.    H.  Mttller  gives  an  elaborate       fruchtung,'  &c.  p.  247. 


Chap.  V.  PIStJM  SATIVUM.  161 

suppose  that  the  fertilisation  of  these  flowers  is  effected  by  the 
carriage  of  pollen  from  one  to  the  other."  Notwithstanding  these 
manifest  provisions  for  cross-fertilisation,  varieties  which  have 
been  cultivated  for  very  many  successive  generations  in  close 
proximity,  although  flowering  at  the  same  time,  remain  pure.  I 
have  elsewhere  *  given  evidence  on  this  head,  and  if  required 
could  give  more.  There  can  hardly  be  a  doubt  that  some  of 
Knight's  varieties,  which  were  originally  produced  by  an  artificial 
cross  and  were  very  vigorous,  lasted  for  at  least  sixty  years,  and 
during  all  these  years  were  self-fertilised ;  for  had  it  been  other- 
wise, they  would  not  have  kept  true,  as  the  several  varieties 
are  generally  grown  near  together.  Most  of  the  varieties,  how- 
ever, endure  for  a  shorter  period ;  and  this  may  be  in  part  due 
to  their  weakness  of  constitution  from  long-continued  self- 
fertilisation. 

It  is  remarkable,  considering  that  the  flowers  secrete  much 
nectar  and  afford  much  pollen,  how  seldom  they  are  visited  by 
insects  either  in  England  or,  as  H.  Muller  remarks,  in  North 
Germany.  I  have  observed  the  flowers  for  the  last  thirty  years, 
and  in  all  this  time  have  only  thrice  seen  bees  of  the  proper  kind  at 
work  (one  of  them  being  Bornbus  muscorum),  such  as  were  suf- 
ficiently powerful  to  depress  the  keel,  so  as  to  get  the  undersides  of 
their  bodies  dusted  with  pollen.  These  bees  visited  several  flowers, 
and  could  hardly  have  failed  to  cross-fertilise  them.  Hive-bees 
and  other  small  kinds  sometimes  collect  pollen  from  old  and 
already  fertilised  flowers,  but  this  is  of  no  account.  The  rarity 
of  the  visits  of  efficient  bees  to  this  exotic  plant  is,  I  believe,  the 
chief  cause  of  the  varieties  so  seldom  intercrossing.  That  a 
cross  does  occasionally  take  place,  as  might  be  expected  from  what 
has  just  been  stated,  is  certain,  from  the  recorded  cases  of  the  direct 
action  of  the  pollen  of  one  variety  on  the  seed-coats  of  another,  f 
The  late  Mr.  Masters,  who  particularly  attended  to  the  raising  of 
new  varieties  of  peas,  was  convinced  that  some  of  them  had 
originated  from  accidental  crosses.  But  as  such  crosses  are 
rare,  the  old  varieties  would  not  often  be  thus  deteriorated,  more 
especially  as  plants  departing  from  the  proper  type  are  generally 
rejected  by  those  who  collect  seed  for  sale.  There  is  another 
cause  which  probably  tends  to  render  cross-fertilisation  rare, 


*  'Variation    of  Animals  and  f  'Var.  under  Domestication,' 

Plants      under      Domestication,'       chap.  xi.  2nd  edit.  vol.  i.  p.  428. 
chap.  ix.  2nd  edit.  vol.  i.  p.  348. 


162 


PISUM   SATIVUM. 


Chap.  V. 


namely,  the  early  age  at  which  the  pollen-tubes  are  exserted ; 
eight  flowers  not  fully  expanded  were  examined,  and  in  seven  of 
these  the  pollen-tubes  were  in  this  state ;  but  they  had  not  as 
yet  penetrated  the  stigma.  Although  so  few  insects  visit  the 
flowers  of  the  pea  in  this  country  or  in  North  Germany,  and 
although  the  anthers  seem  here  to  open  abnormally  soon,  it  does 
not  follow  that  the  species  in  its  native  country  would  be  thus 
circumstanced. 

Owing  to  the  varieties  having  been  self-fertilised  for  many 
generations,  and  to  their  having  been  subjected  in  each  genera- 
tion to  nearly  the  same  conditions  (as  will  be  explained  in  a 
future  chapter),  I  did  not  expect  that  a  cross  between  two  such 
plants  would  benefit  the  offspring  ;  and  so  it  proved  on  trial.  In 
1867  I  covered  up  several  plants  of  the  Early  Emperor  pea,  which 
was  not  then  a  very  new  variety,  so  that  it  must  already  have 
been  propagated  by  self-fertilisation  for  at  least  a  dozen  genera- 
tions. Some  flowers  were  crossed  with  pollen  from  a  distinct 
plant  growing  in  the  same  row,  and  others  were  allowed  to 
fertilise  themselves  under  a  net.  The  two  lots  of  seeds  thus 
obtained  were  sown  on  opposite  sides  of  two  large  pots,  but  only 
four  pairs  came  up  at  the  same  time.  The  pots  were  kept  in  the 
greenhouse.  The  seedlings  of  both  lots  when  between  6  and  7 
inches  in  height  were  equal.  When  nearly  full-grown  they 
were  measured,  as  in  the  following  table  : —  \ 

Table  LVII. 

Pisum  sativum. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
35 

Inches. 
29f 

II. 

31 1 

35 

37 

51 

45 
33 

Total  in  inches. 

138-50 

158-75 

The  average  height  of  the  four  crossed  plants  is  here  34-62, 
and  that  of  the  four  self-fertilised  plants  39  ■  68,  or  as  100  to  115. 
So  that  the  crossed  plants,  far  from  beating  the  self-fertilised, 
were  completely  beaten  by  them. 


Chap.  V.  SAROTHAMNUS   SCOPARIUS.  163 

There  can  be  no  doubt  that  the  result  would  have  been 
widely  different,  if  any  two  varieties  out  of  the  numberless  ones 
which  exist  had  been  crossed.  Notwithstanding  that  both  had 
been  self-fertilised  for  many  previous  generations,  each  would 
almost  certainly  have  possessed  its  own  peculiar  constitution; 
and  this  degree  of  differentiation  would  have  been  sufficient  to 
make  a  cross  highly  beneficial.  I  have  spoken  thus  confidently 
of  the  benefit  which  would  have  been  derived  from  crossing  any 
two  varieties  of  the  pea  from  the  following  facts:  Andrew 
Knight  in  speaking  of  the  results  of  crossing  reciprocally  very 
tall  and  short  varieties,  says,*  "I  had  in  this  experiment  a 
striking  instance  of  the  stimulative  effects  of  crossing  the  breeds ; 
for  the  smallest  variety,  whose  height  rarely  exceeded  2  feet, 
was  increased  to  6  feet;  whilst  the  height  of  the  large  and 
luxuriant  kind  was  very  little  diminished."  Recently  Mr.  Laxton 
has  made  numerous  crosses,  and  everyone  has  been  astonished  at 
the  vigour  and  luxuriance  of  the  new  varieties  which  he  has  thus 
raised  and  afterwards  fixed  by  selection.  He  gave  me  seed-peas 
produced  from  crosses  between  four  distinct  kinds ;  and  the 
plants  thus  raised  were  extraordinarily  vigorous,  being  in  each 
case  from  1  to  2  or  even  3  feet  taller  than  the  parent-forms, 
which  were  raised  at  the  same  time  close  alongside.  But  as 
I  did  not  measure  their  actual  height  I  cannot  give  the  exact 
ratio,  but  it  must  have  been  at  least  as  100  to  75.  A  similar 
trial  was  subsequently  made  with  two  other  peas  from  a  different 
cross,  and  the  result  was  nearly  the  same.  For  instance,  a  crossed 
seedling  between  the  Maple  and  Purple-podded  pea  was  planted 
in  poor  soil  and  grew  to  the  extraordinary  height  of  116  inches ; 
whereas  the  tallest  plant  of  either  parent  variety,  namely,  a 
Purple-podded  pea,  was  only  70  inches  in  height ;  or  as  100  to  60. 

Sarothamnus  SCOPARIUS. 

Bees  incessantly  visit  the  flowers  of  the  common  Broom,  and 
these  are  adapted  by  a  curious  mechanism  for  cross-fertilisation. 
When  a  bee  alights  on  the  wing-petals  of  a  young  flower,  the 
keel  is  slightly  opened  and  the  short  stamens  spring  out,  which 
rub  their  pollen  against  the  abdomen  of  the  bee.  If  a  rather 
older  flower  is  visited  for  the  first  time  (or  if  the  bee  exerts  great 
force  on  a  younger  flower),  the  keel  opens  along  its  whole 
length,  and  the  longer  as  well  as  the  shorter  stamens,  together 

*  '  Philosophical  Transactions,'  X799,  p.  200. 


L64  SAROTHAMNUS   SCOPARIUS.  Chap.  V. 

with  the  much  elongated  curved  pistil,  spring  forth  with  violence. 
The  flattened,  spoon-like  extremity  of  the  pistil  rests  for  a  time 
on  the  back  of  the  bee,  and  leaves  on  it  the  load  of  pollen  with 
which  it  is  charged.  As  soon  as  the  bee  flies  away,  the  pistil 
instantly  curls  round,  so  that  the  stigmatic  surface  is  now  up- 
turned and  occupies  a  position,  in  which  it  would  be  rubbed 
against  the  abdomen  of  another  bee  visiting  the  same  flower. 
Thus,  when  the  pistil  first  escapes  from  the  keel,  the  stigma 
is  rubbed  against  the  back  of  the  bee,  dusted  with  pollen 
from  the  longer  stamens,  either  of  the  same  or  another  flower ; 
and  afterwards  against  the  lower  surface  of  the  bee  dusted 
with  pollen  from  the  shorter  stamens,  which  is  often  shed  a 
day  or  two  before  that  from  the  longer  stamens.  *  By  this 
mechanism  cross-fertilisation  is  rendered  almost  inevitable,  and 
we  shall  immediately  see  that  pollen  from  a  distinct  plant  is 
more  effective  than  that  from  the  same  flower.  I  need  only  add 
that,  according  to  H.  Miiller,  the  flowers  do  not  secrete  nectar, 
and  he  thinks  that  bees  insert  their  proboscides  only  in  the  hope 
of  finding  nectar ;  but  they  act  in  this  manner  so  frequently  and 
for  so  long  a  time  that  I  cannot  avoid  the  belief  that  they 
obtain  something  palatable  within  the  flowers. 

If  the  visits  of  bees  are  prevented,  and  if  the  flowers  are 
not  dashed  by  the  wind  against  any  object,  the  keel  never 
opens,  so  that  the  stamens  and  pistil  remain  enclosed.  Plants 
thus  protected  yield  very  few  pods  in  comparison  with  those 
produced  by  neighbouring  uncovered  bushes,  and  sometimes 
none  at  all.  I  fertilised  a  few  flowers  on  a  plant  growing 
almost  in  a  state  of  nature  with  pollen  from  another  plant 
close  alongside,  and  the  four  crossed  capsules  contained  on 
an  average  9*2  seeds.  This  large  number  no  doubt  was  due 
to  the  bush  being  covered  up,  and  thus  not  exhausted  by 
producing  many  pods ;  for  fifty  pods  gathered  from  an  adjoining 
plant,  the  flowers  of  which  had  been  fertilised  by  the  bees, 
contained  an  average  of  only  7  "14  seeds.  Ninety-three  pods 
spontaneously  self-fertilised  on  a  large  bush  which  had  been 
covered  up,  but  had  been  much  agitated  by  the  wind,  contained 
an  average  of  2*93  seeds.    Ten  of  the  finest  of  these  ninety- 


*  These  observations  have  been  ix.  1866,  p.  358.     H.  Miiller  has 

quoted  in  an  abbreviated  form  by  since  published  a  full  and  excel- 

the    Rev.    G.   Henslow,    in    the  lent  account  of  the  flower  in  his 

'Journal  of  Linn.  Soc.  Bot.'  vol.  * Befruchtung,'  &c.  p.  240. 


Chap.  V. 


SAROTHAMXUS   SCOPAEIUS. 


165 


three  capsules  yielded  an  average  of  4  •  30  seeds,  that  is  less  than 
half  the  average  number  in  the  four  artificially  crossed  capsules. 
The  ratio  of  7'14  to  2 -93,  or  as  100  to  41,  is  probably  the 
fairest  for  the  number  of  seeds  per  pod,  yielded  by  naturally- 
crossed  and  spontaneously  self-fertilised  flowers.  The  crossed 
seeds  compared  with  an  equal  number  of  the  spontaneously  self- 
fertilised  seeds  were  heavier,  in  the  ratio  of  100  to  88.  We  thus 
see  that  besides  the  mechanical  adaptations  for  cross-fertilisation, 
the  flowers  are  much  more  productive  with  pollen  from  a 
distinct  plant  than  with  their  own  pollen. 

Eight  pairs  of  the  above  crossed  and  self-fertilised  seeds,  after 
they  had  germinated  on  sand,  were  planted  (1867)  on  the 
opposite  sides  of  two  large  pots.  "When  several  of  the  seedlings 
were  an  inch  and  a  half  in  height,  there  was  no  marked  difference 
between  the  two  lots.  But  even  at  this  early  age  the  leaves  of 
the  self-fertilised  seedlings  were  smaller  and  of  not  so  bright  a 
green  as  those  of  the  crossed  seedlings.  The  pots  were  kept  in 
the  greenhouse,  and  as  the  plants  on  the  following  spring  (1868) 
looked  unhealthy  and  had  grown  but  little,  they  were  plunged, 
still  in  their  pots,  into  the  open  ground.  The  plants  all  suffered 
much  from  the  sudden  change,  especially  the  self-fertilised,  and 
two  of  the  latter  died.  The  remainder  were  measured,  and  I 
give  the  measurements  in  the  following  table,  because  I  have 
not  seen  in  any  other  species  so  great  a  difference  between  the 
crossed  and  self-fertilised  seedlings  at  so  early  an  age. 


Table  LVLTI. 
Sarothamnus  scoparius  (very  young  plants). 


No.  of  Pot 

Crossed  Plants.         Self-fertilUed  Plants. 

I. 

Inches.                           Inches. 

n               21 

2                                1 

n. 

2                                 1| 
2|                               1 

0|                         oj 

Total  in  inches. 

17-5                            3-0 

The  six  crossed  plants  here  average  2-91,  and  the  six  self- 


166 


SAEOTHAMNUS   SCOPAEIUS. 


Chap.  V. 


fertilised  1  ■  33  inches  in  height ;  so  that  the  former  were  more 
than  twice  as  high  as  the  latter,  or  as  100  to  46. 

In  the  spring  of  the  succeeding  year  (1869)  the  three  crossed 
plants  in  Pot  I.  had  all  grown  to  nearly  a  foot  in  height,  and  they 
had  smothered  the  three  little  self-fertilised  plaDts  so  completely 
that  two  were  dead ;  and  the  third,  only  an  inch  and  a  half 
in  height,  was  dying.  It  should  be  remembered  that  these 
plants  had  been  bedded  out  in  their  pots,  so  that  they  were 
subjected  to  very  severe  competition.  This  pot  was  now  thrown 
away. 

The  six  plants  in  Pot  II.  were  all  alive.  One  of  the  self- 
fertilised  was  an  inch  and  a  quarter  taller  than  any  one  of  the 
crossed  plants ;  but  the  other  two  self-fertilised  plants  were  in  a 
very  poor  condition.  I  therefore  resolved  to  leave  these  plants  to 
struggle  together  for  some  years.  By  the  autumn  of  the  same 
year  (1869)  the  self-fertilised  plant  which  had  been  victorious 
was  now  beaten.  The  measurements  are  shown  in  the  following 
table : — 

Table  LIX. 
Pot  II. — Sarothamnus  scoparius. 


Crossed  Plants.       :  Self-fertilised  Plants. 

Inches. 
15 1 

n 

81 

Inches. 

13| 

3 

2| 

The  same  plants  were  again  measured  in  the  autumn  of  the 
following  year,  1870. 

Table  LX. 
Pot  II. — Sarothamnus  scoparius. 


Crossed  Plants. 

Self-fertilised  Plants. 

Inches. 
26 1 

14 

Inches. 

141 

HI 

9§ 

56-75 

35-50 

Chap.  V.  ONONIS   MINUTISSIMA.  167 

The  three  crossed  plants  now  averaged  18'  91,  and  the  three 
self-fertilised  11  ■  83  inches  in  height ;  or  as  100  to  63.  The  three 
crossed  plants  in  Pot  I.,  as  already  shown,  had  beaten  the  three 
self -fertilised  plants  so  completely,  that  any  comparison  between 
them  was  superfluous. 

The  winter  of  1870-1871  was  severe.  In  the  spring  the  three 
crossed  plants  in  Pot  II.  had  not  even  the  tips  of  their  shoots  in 
the  least  injured,  whereas  all  three  self-fertilised  plants  were 
killed  half-way  down  to  the  ground ;  and  this  shows  how  much 
more  tender  they  were.  In  consequence  not  one  of  these  latter 
plants  bore  a  single  flower  during  the  ensuing  summer  of  1871, 
whilst  all  three  crossed  plants  flowered. 

Ononis  minutisshia. 

This  plant,  of  which  seeds  were  sent  me  from  North  Italy,  pro- 
duces, besides  the  ordinary  papilionaceous  flowers,  minute,  imper- 
fect, closed  or  cleistogene  flowers,  which  can  never  be  cross-ferti- 
lised, but  are  highly  self-fertile.  Some  of  the  perfect  flowers  were 
crossed  with  pollen  from  a  distinct  plant,  and  six  capsules  thus 
produced  yielded  on  an  average  3  ■  66  seeds,  with  a  maximum 
of  five  in  one.  Twelve  perfect  flowers  were  marked  and  allowed 
to  fertilise  themselves  spontaneously  under  a  net,  and  they 
yielded  eight  capsules,  containing  on  an  average  2  ■  38  seeds,  with 
a  maximum  of  three  seeds  in  one.  So  that  the  crossed  and  self- 
fertilised  capsules  from  the  perfect  flowers  yielded  seeds  in  the 
proportion  of  100  to  65.  Fifty-three  capsules  produced  by  the 
cleistogene  flowers  contained  on  an  average  4*1  seeds,  so  that 
these  were  the  most  productive  of  all;  and  the  seeds  them- 
selves looked  finer  even  than  those  from  the  crossed  perfect 
flowers. 

The  seeds  from  the  crossed  perfect  flowers  and  from  the  self- 
fertilised  cleistogene  flowers  were  allowed  to  germinate  on  sand ; 
but  unfortunately  only  two  pairs  germinated  at  the  same  time. 
These  were  planted  on  the  opposite  sides  of  the  same  pot,  which 
was  kept  in  the  greenhouse.  In  the  summer  of  the  same  year, 
when  the  seedlings  were  about  4^  inches  in  height,  the  two  lots 
were  equal.  In  the  autumn  of  the  following  year  (1868)  the  two 
crossed  plants  were  of  exactly  the  same  height,  viz.,  llf  inches, 
and  the  two  self  fertilised  plants  12|-  and  7f  inches ;  so  that  one 
of  the  self-fertilised  exceeded  considerably  in  height  all  the  others. 
By  the  autumn  of  1869  the  two  crossed  plants  had  acquired  the 


168 


SUMMARY   ON   THE   LEGUMINOS.E. 


Chap.  V. 


supremacy ;  their  height  being  16*  and  15|,  whilst  that  of  the 
two  self-fertilised  plants  was  14f  and  llf  inches. 
By  the  autumn  of  1870,  the  heights  were  as  follows  :— 

Table  LXI. 

Ononis  minutissima. 


Crossed  Plants. 

Self-fertilised  Plant3. 

Inches. 
20  % 
19§ 

Inches. 
17 1 
17  § 

39-63 

34-75 

So  that  the  mean  height  of  the  two  crossed  plants  was  19 '  81, 
and  that  of  the  two  self- fertilised  17  ■  37  inches ;  or  as  100  to  88. 
It  should  be  remembered  that  the  two  lots  were  at  first  equal  in 
height;  that  one  of  the  self-fertilised  plants  then  had  the  advan- 
tage, the  two  crossed  plants  being  at  last  victorious. 

Summary  on  the  Leguminosse. — Six  genera  in  this 
family  were  experimented  on,  and  the  results  are  in 
some  respects  remarkable.  The  crossed  plants  of  the 
two  species  of  Lupinus  were  conspicuously  superior  to 
the  self-fertilised  plants  in  height  and  fertility ;  and 
when  grown  under  very  unfavourable  conditions,  in 
vigour.  The  scarlet-runner  (Phaseolus  multijlorus)  is 
partially  sterile  if  the  visits  of  bees  are  prevented,  and 
there  is  reason  to  believe  that  varieties  growing  near 
one  another  intercross.  The  five  crossed  plants,  how- 
ever, exceeded  in  height  the  five  self-fertilised  only 
by  a  little.  Phaseolus  vulgaris  is  perfectly  self-fertile ; 
nevertheless,  varieties  growing  in  the  same  garden 
sometimes  intercross  largely.  The  varieties  of  Lathyrus 
odoratus,  on  the  other  hand,  appear  never  to  intercross 
in  this  country  ;  and  though  the  flowers  are  not  often 
visited  by  efficient  insects,  I  cannot  account  for  this 
fact,  more  especially  as  the  varieties  are  believed  to 


Chap.  V.  CLAKKIA   ELEGANS.  169 

intercross  in  North.  Italy.  Plants  raised  from  a  cross 
between  two  varieties,  differing  only  in  the  colour  of 
their  flowers,  grew  much  taller  and  were  under  un- 
favourable conditions  more  vigorous  than  the  self -ferti- 
lised plants ;  they  also  transmitted,  when  self-fertilised, 
their  superiority  to  their  offspring.  The  many  varieties 
of  the  common  Pea  (Pisum  sativum),  though  growing  in 
close  proximity,  very  seldom  intercross  ;  and  this  seems 
due  to  the  rarity  in  this  country  of  the  visits  of  bees 
sufficiently  powerful  to  effect  cross-fertilisation.  A 
cross  between  the  self-fertilised  individuals  of  the  same 
variety  does  no  good  whatever  to  the  offspring ;  whilst 
a  cross  between  distinct  varieties,  though  closely  allied, 
does  great  good,  of  which  we  have  excellent  evidence. 
The  flowers  of  the  Broom  (Sarothamnus)  are  almost 
sterile  if  they  are  not  disturbed  and  if  insects  are  ex- 
cluded. The  pollen  from  a  distinct  plant  is  more 
effective  than  that  from  the  same  flower  in  producing 
seeds.  The  crossed  seedlings  have  an  enormous  advan- 
tage over  the  self-fertilised  when  grown  together  in 
close  competition.  Lastly,  only  four  plants  of  the 
Ononis  mmutissima  were  raised ;  but  as  these  were 
observed  during  their  whole  growth,  the  advantage  of 
the  crossed  over  the  self-fertilised  plants  may,  I  think, 
be  fully  trusted. 

XV.  ONAGEACE^.— Clarkia  elegans. 

Owing  to  the  season  being  very  unfavourable  (1867),  few  of 
the  flowers  which  I  fertilised  formed  capsules ;  twelve  crossed 
flowers  produced  only  four,  and  eighteen  self- fertilised  flowers 
yielded  only  one  capsule.  The  seeds  after  germinating  on  sand 
were  planted  in  three  pots,  but  all  the  self-fertilised  plants  died 
in  one  of  them.  When  the  two  lots  were  between  4  and  5 
inches  in  height,  the  crossed  began  to  show  a  slight  superiority 
over  the  self-fertilised.  When  in  full  flower  they  were  measured, 
with  the  following  result : — 


L70 


BARTONIA   AUREA. 

Table  LXII. 

Clarkia  elegans. 


Chap.  V 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
40 1 
35 
25 

Inches. 
33 
24 
23 

II. 

33 1 

30 1 

Total  in  inches. 

134-0 

110-5 

The  average  height  of  the  four  crossed  plants  is  33  ■  5,  and 
that  of  the  four  self-fertilised  plants  27 "  62  inches,  or  as  100  to 
82.  The  crossed  plants  altogether  produced  105  and  the  self- 
fertilised  plants  63  capsules ;  or  as  100  to  60.  Iu  both  pots  a 
self-fertilised  plant  flowered  before  any  one  of  the  crossed  plants. 

XVI.  LOASAOEiE.— Bartonia  attrea. 

Some  flowers  were  crossed  and  self-fertilised  in  the  usual 
manner  during  two  seasons ;  but  as  I  reared  on  the  first  occasion 

Table  LXIH. 
Bartonia  aurea. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
31 

Inches. 
37 

II. 

18| 

20 1 

III. 

193 

40$ 

IV. 

25 
36 

35 
15| 

V. 

31 
16 

18 

VI. 

20 

32 1 

Total  in  inches. 

197-0 

210-5 

Chap.  V. 


PASSIFLOEA    GRACILIS. 


171 


only  two  pairs,  the  results  are  given  together.  On  both  occasions 
the  crossed  capsules  contained  slightly  more  seeds  than  the  self- 
fertilised.  During  the  first  year,  when  the  plants  were  about 
7  inches  in  height,  the  self-fertilised  were  the  tallest,  and  in  the 
second  year  the  crossed  were  the  tallest.  When  the  two  lots  were 
in  full  flower  they  were  measured,  as  in  the  preceding  table. 

The  average  height  of  the  eight  crossed  plants  is  24  ■  62,  and  that 
of  the  eight  self-fertilised  26  "31  inches;  or  as  100  to  107.  So  that 
the  self-fertilised  had  a  decided  advantage  over  the  crossed.  But 
the  plants  from  some  cause  never  grew  well,  and  finally  became 
so  unhealthy  that  only  three  crossed  and  three  self-fertilised 
plants  survived  to  set  any  capsules,  and  these  were  few  in  number. 
The  two  lots  seemed  to  be  about  equally  unproductive. 

XVII.  PASSIFLOEACE.E.— Passiflora  gracilis. 

This  annual  species  produces  spontaneously  numerous  fruits 
when  insects  are  excluded,  and  behaves  in  this  respect  very 
differently  from  most  of  the  other  species  in  the  genus,  which 
are  extremely  sterile  unless  fertilised  with  pollen  from  a  distinct 
plant.*  Fourteen  fruits  from  crossed  flowers  contained  on  an 
average  24"  14  seeds.  Fourteen  fruits  (two  poor  ones  being 
rejected),  spontaneously  self- fertilised  under  a  net,  contained  on 
an  average  20 '58  seeds  per  fruit;  or  as  100  to  85.  These  seeds 
were  sown  on  the  opposite  sides  of  three  pots,  but  only  two  pairs 
came  up  at  the  same  time ;  and  therefore  a  fair  judgment  cannot 
be  formed. 

Table  LXIV. 
Passiflora  gracilis. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
56 

Inches. 
38 

II. 

42 

64 

Total  in  inches. 

98 

102 

The  mean  of  the  two  crossed  is  49  inches,  and  that  of  the  two 
self-fertilised  51  inches ;  or  as  100  to  104. 


*   'Variation  of  Animals  and      chap.  xvii.  2nd   edit.  vol.   ii.   p. 
Plants     under     Domestication, '       118, 


172 


SCABIOSA   ATRO-PURPUREA. 


Chap.  V. 


XVIH.  UMBELLIFEK^].— Apium  petkoselintjm. 

The  Umbelliferse  are  proterandrous,  and  can  hardly  fail  to  be 
cross-fertilised  by  the  many  flies  and  small  Hymenoptera  which 
visit  the  flowers.*  A  plant  of  the  common  parsley  was  covered 
by  a  net,  and  it  apparently  produced  as  many  and  as  fine 
spontaneously  self-fertilised  fruits  or  seeds  as  the  adjoining 
uncovered  plants.  The  flowers  on  the  latter  were  visited  by  so 
many  insects  that  they  must  have  received  pollen  from  one 
another.  Some  of  these  two  lots  of  seeds  were  left  on  sand,  but 
nearly  all  the  self-fertilised  seeds  germinated  before  the  others, 
so  that  I  was  forced  to  throw  all  away.  The  remaining  seeds 
were  then  sown  on  the  opposite  sides  of  four  pots.  At  first  the 
self-fertilised  seedlings  were  a  little  taller  in  most  of  the  pots 
than  the  naturally  crossed  seedlings,  and  this  no  doubt  was  due 
to  the  self-fertilised  seeds  having  germinated  first.  But  in 
the  autumn  all  the  plants  were  so  equal  that  it  did  not  seem 
worth  while  to  measure  them.  In  two  of  the  pots  they  were 
absolutely  equal ;  in  a  third,  if  there  was  any  difference,  it  was 
in  favour  of  the  crossed  plants,  and  in  a  somewhat  plainer 
manner  in  the  fourth  pot.  But  neither  side  had  any  substantial 
advantage  over  the  other ;  so  that  in  height  they  may  be  said 
to  be  as  100  to  100. 


XIX.  DIPSACEiE.— Scabiosa  atbo-purptjrea. 
The  flowers,  which  are  proterandrous,  were  fertilised  during 

Table  LXV. 

Scabiosa  atro-purpurea. 


No.  of  Pot. 

Crossed  Plants. 

Self- fertilised  Plants. 

I. 

Inches. 
14 

Inches. 
20 

II. 

15 

l4#  -;^ 

HI. 

21 
18| 

14       . 
13 

Total  in  inches. 

68-5 

*""»         61-5 

*  H.  Miiller, '  Befruchtung,'  &c. 
p.  96.  According  to  M.  Mustel 
(as  stated  by  Godron,  '  De  l'Es- 


pece,'  torn.  ii.p.  58, 1859),  varieties 
of  the  carrot  growing  near  each 
other  readily  intercross. 


Chap.  V.  LACTUCA  SATIVA.  173 

the  unfavourable  season  of  1867,  so  that  I  got  few  seeds, 
especially  from  the  self-fertilised  heads,  which  were  extremely 
sterile.  The  crossed  and  self-fertilised  plants  raised  from  these 
seeds  were  measured  before  they  were  in  full  flower,  as  in  the 
preceding  table. 

The  four  crossed  plants  averaged  17 "  12,  and  the  four  self-fer- 
tilised ]5-37  inches  in  height;  or  as  100  to  90.  One  of  the  self- 
fertilised  plants  in  Pot  III.  was  killed  by  an  accident,  and  its 
fellow  pulled  up ;  so  that  when  they  were  again  measured  to  the 
summits  of  their  flowers,  there  were  only  three  on  each  side ; 
the  crossed  now  averaged  in  height  32  ■  83,  and  the  self-fertilised 
30-16  inches;  or  as  100  to  92. 

XX.  COMPOSITE.— Lactuca  sativa. 

Three  plants  of  Lettuce*  (Great  London  Cos  var.)  grew  close 
together  in  my  garden ;  one  was  covered  by  a  net,  and  produced 
self-fertilised  seeds,  the  other  two  were  allowed  to  be  naturally 
crossed  by  insects;  but  the  season (1867)  was  unfavourable,  and 
I  did  not  obtain  many  seeds.  Only  one  crossed  and  one  self- 
fertilised  plant  were  raised  in  Pot  I.,  and  their  measurements  are 
given  in  the  following  table  (LXVL).  The  flowers  on  this  one 
self-fertilised  plant  were  again  self-fertilised  under  a  net,  not 
with  pollen  from  the  same  floret,  but  from  other  florets  on  the 
same  head.  The  flowers  on  the  two  crossed  plants  were  left  to 
be  crossed  by  insects,  but  the  process  was  aided  by  some  pollen 
being  occasionally  transported  by  me  from  plant  to  plant.  These 
two  lots  of  seeds,  after  germinating  on  sand,  were  planted  in 
pairs  on  the  opposite  sides  of  Pots  II.  and  III.,  which  were  at 
first  kept  in  the  greenhouse  and  then  turned  out  of  doors.  The 
plants  were  measured  when  in  full  flower.  The  following  table, 
therefore,  includes  plants  belonging  to  two  generations.  When 
the  seedlings  of  the  two  lots  were  only  5  or  6  inches  in  height 
they  were  equal.  In  Pot  ILL  one  of  the  self-fertilised  plants 
died  before  flowering,  as  has  occurred  in  so  many  other  cases. 


*  The    Composite    are    well-  It  is  very  improbable  that  all  the 

adapted  for  cross-fertilisation,  but  varieties  which  were  thus  culti- 

a    nurseryman    on   whom  I  can  vated  near  together   flowered  at 

rely,  told  me  that  he  had  been  in  different  times ;  but  two  which  I 

the  hnbit  of  sowing  several  kinds  selected    by   hazard    and    sowed 

of  lettuce   near  together  for  the  near  each  other  did  not  flower  at 

sake  of  seed,  and  had  never  ob-  the  same   time  ;    and    my  trial 

served  that  they  became  crossed.  failed. 


174 


SPEOULAKIA   SPECULUM. 


Chap.  V. 


Table  LXVI. 

Lactuca  saiiva. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

First  generation, 

planted  in  open 

ground. 

Inches. 
27 
25 

Inches. 
21  | 
20 

II. 

Second  generation, 

planted  in  open 

ground. 

29 1 

17 1 
12| 

24 
10 
11 

III. 

Second  generation, 
kept  in  the  pot. 

14 

103 

Q4 
0 

Total  in  inches. 

136 

96 

The  average  height  of  the  seven  crossed  plants  is  19  ■  43,  and. 
that  of  the  six  self-fertilised  plants  16  inches ;  or  as  100  to  82. 


XXI.  CAMPANULACEiE.— Speoulaeia  speculum. 

In  the  closely  allied  genus,  Campanula,  in  wbich  Specnlaria 
was  formerly  included,  the  anthers  shed  at  an  early  period  their 
pollen,  and  this  adheres  to  the  collecting  hairs  which  surround 
the  pistil  beneath  the  stigma ;  so  that  without  some  mechanical 
aid  the  flowers  cannot  be  fertilised.  For  instance,  I  covered  up 
a  plant  of  Campanula  carpathica,  and  it  did  not  produce  a  single 
capsule,  whilst  the  surrounding  uncovered  plants  seeded  pro- 
fusely. On  the  other  hand,  the  present  species  of  Specularia 
appears  to  set  almost  as  many  capsules  when  covered  up,  as 
when  left  to  the  visits  of  the  Diptera,  which,  as  far  as  I  have 
seen,  are  the  only  insects  that  frequent  the  flowers.*  I  did  not 
ascertain  whether  the  naturally  crossed  and  spontaneously  self- 
fertilised  capsules  contained  an  equal  number  of  seeds,  but  a 
comparison   of   artificially  crossed   and    self-fertilised    flowers, 


*  It  has  long  been  known  that 
another  species  of  the  genus, 
Specularia     perfoliata,    produces 


cleistogene    as    well     as    perfect 
flowers,   and    the    former  are   of 

course  self-fertile. 


Chap.  V. 


SPECULARIA   SPECULUM. 


175 


showed  that  the  former  were  probably  the  most  productive.  It 
appears  that  this  plant  is  capable  of  producing  a  large  number 
of  self-fertilised  capsules  owing  to  the  petals  closing  at  night,  as 
well  as  during  cold  weather.  In  the  act  of  closing,  the  margins 
of  the  petals  become  reflexed,  and  their  inwardly  projecting 
midribs  then  pass  between  the  clefts  of  the  stigma,  and  in  doing 
so  push  the  pollen  from  the  outside  of  the  pistil  on  to  the 
stigmatic  surfaces.* 

Twenty  flowers  were  fertilised  by  me  with  their  own  pollen, 
but  owing  to  the  bad  season,  only  six  capsules  were  produced  ■ 
they  contained  on  an  average  21*  7  seeds,  with  a  maximum  of 
forty-eight  in  one.  Fourteen  flowers  were  crossed  with  pollen 
from  another  plant,  and  these  produced  twelve  capsules,  contain- 
ing on  an  average  30  seeds,  with  a  maximum  in  one  of  fifty- 
seven  feeds ;  so  that  the  crossed  seeds  were  to  the  self-fertilised 
from  an  equal  number  of  capsules  as  100  to  72.  The  former 
were  also  heavier  than  an  equal  number  of  self-fertilised  seeds, 
in  the  ratio  of  100  to  86.  Thus,  whether  we  judge  by  the  number 
of  capsules  produced  from  an  equal  number  of  flowers,  or  by  the 
average  number  of  the  contained  seeds,  or  the  maximum  number 
in  any  one  capsule,  or  by  their  weight,  crossing  does  great  good 
in  comparison  with  self-fertilisation.    The  two  lots  of  seeds  were 


Table  LXVII. 

Spectduria  speculum. 


No.  of  Pot. 

Tallest  Crossed  Plant 
in  each  Pot. 

Tallest  Self-fertilised 
Plant  in  each  Pot. 

I. 

Inches. 
18 

Inches. 
15§ 

II. 

17 

19 

m. 

22ft 

18 

IV. 

20 

23 

Total  in  inches. 

77-13 

75-75 

*  Mr.  Meehan  has  lately  shown 
('  Proc.  Acad.  Nat.  Sc.  Philadel- 
phia,' May  16,  1876,  p.  84)  that 
the  closing  of  the  flowers  of  Clay- 


tonia  virginica  and  Ranunculus  bulr 
bosus  during  the  night  causes  their 
self-fertilisation. 


176  LOBELIA  EAMOSA.  Chap.  V. 

sown  on  the  opposite  sides  of  four  pots ;  but  the  seedlings  were 
not  sufficiently  thinned.  Only  the  tallest  plant  on  each  side  was 
measured,  when  fully  grown.  The  measurements  are  given  in 
the  preceding  table.  In  all  four  pots  the  crossed  plants  flowered 
first.  When  the  seedlings  were  only  about  an  inch  and  a  half  in 
height  both  lots  were  equal. 

The  four  tallest  crossed  plants  averaged  19  -28,  and  the  four 
tallest  self-fertilised  18 "93  inches  in  height;  or  as  100  to  98. 
So  that  there  was  no  difference  worth  speaking  of  between  the 
two  lots  in  height ;  though  other  great  advantages  are  derived, 
as  we  have  seen,  from  cross-fertilisation.  From  being  grown  in 
pots  and  kept  in  the  greenhouse,  none  of  the  plants  produced 
any  capsules. 

Lobelia  kamosa.* 
Var.  Snow-flake. 

The  well-adapted  means  by  which  cross-fertilisation  is  en- 
sured in  this  genus  have  been  described  by  several  authors,  f 
The  pistil  as  it  slowly  increases  in  length  pushes  the  pollen 
out  of  the  conjoined  anthers,  by  the  aid  of  a  ring  of  bristles ;  the 
two  lobes  of  the  stigma  being  at  this  time  closed  and  incapable 
of  fertilisation.  The  extrusion  of  the  pollen  is  also  aided  by 
insects,  which  rub  against  the  little  bristles  that  project  from 
the  anthers.  The  pollen  thus  pushed  out  is  carried  by  insects 
to  the  older  flowers,  in  which  the  stigma  of  the  now  freely 
projecting  pistil  is  open  and  ready  to  be  fertilised.  I  proved 
the  importance  of  the  gaily-coloured  corolla,  by  cutting  off  the 
large  lower  petal  of  several  flowers  of  Lobelia  erinus ;  and  these 
flowers  were  neglected  by  the  hive-bees  which  were  incessantly 
visiting  the  other  flowers. 

A  capsule  was  obtained  by  crossing  a  flower  of  L.  ramosa 


*  I  have    adopted    the    name  Mag.  of  Nat.  Hist.'  vol.  ii.  (4th 

given  to  this  plant  in  the  '  Gar-  series)  1868,  p.  260.    In  the  allied 

deners'  Chronicle,'   1866.     Prof.  genus  Isotoma,  the  curious  spike 

T.   Dyer,  however,   informs    me  which  projects  rectangularly  from 

that  it  probably  is  a  white  variety  the    anthers,    and    which   when 

of  L.  tenuior  of  R.  Brown,  from  shaken  causes  the  pollen  to  fall 

W.  Australia.  on  tbe  back  of  an  entering  insect, 

t  See  tbe  works  of  Hildebrand  seems  to  have    been    developed 

and    Delpino.     Mr.  Farrer    also  from  a  bristle,  like  one  of  those 

has    given    a    remarkably   clear  which  spring  from  the  anthers  in 

description  of  the  mechanism  by  some  of  or  all  tbe  species  of  Lo- 

which  cross-fertilisation  is  effected  belia,  a3  described  by  Mr.  Farrer. 
in  this  genus,  in  tbe  '  Annals  and 


Chap.  V. 


LOBELIA   RAMOSA. 


177 


with  pollen  from  another  plant,  and  two  other  capsules  from 
artificially  self-fertilised  flowers.  The  contained  seeds  were 
sown  on  the  opposite  sides  of  four  pots.  Some  of  the  crossed 
seedlings  which  came  up  before  the  others  had  to  be  pulled  up 
and  thrown  away.  Whilst  the  plants  were  very  small  there  was 
not  much  difference  in  height  between  the  two  lots ;  but  in  Pot 
III.  the  self-fertilised  were  for  a  time  the  tallest.  "When  in  full 
flower  the  tallest  plant  on  each  side  of  each  pot  was  measured, 
and  the  result  is  shown  in  the  following  table.  In  all  four 
pots  a  crossed  plant  flowered  before  any  one  of  its  opponents. 


Table  LXVLTI. 

Lobelia  ramosa  (First  Generation). 


No.  of  Pot. 

Tallest  Crossed  Plant 
in  each  Pot. 

Tallest  Self-fertilised 
Plant  in  each  Pot. 

I. 

Inches. 
22 1 

Inches. 
17 1 

II. 

27 1 

24 

III. 

16$ 

15 

IV. 

22 1 

17 

Total  in  inches. 

89-0 

73-5 

The  four  tallest  crossed  plants  averaged  22  ■  25,  and  the  four 
tallest  self-fertilised  18  ■  37  inches  in  height ;  or  as  100  to  82.  I 
was  surprised  to  find  that  the  anthers  of  a  good  many  of  these 
self-fertilised  plants  did  not  cohere  and  did  not  contain  any 
pollen ;  and  the  anthers  even  of  a  very  few  of  the  crossed  plants 
were  in  the  same  condition.  Some  flowers  on  the  crossed  plants 
were  again  crossed,  four  capsules  being  thus  obtained ;  and  some 
flowers  on  the  self-fertilised  plants  were  again  self-fertilised, 
seven  capsules  being  thus  obtained.  The  seeds  from  both  lots 
were  weighed,  and  it  was  calculated  that  an  equal  number  of 
capsules  would  have  yielded  seed  in  the  proportion  by  weight  of 
100  for  the  crossed  to  60  for  the  self-fertilised  capsules.  So  that 
the  flowers  on  the  crossed  plants  again  crossed  were  much 
more  fertile  than  those  on  the  self-fertilised  plants  again  self- 
fertilised. 


178 


LOBELIA   EAMOSA. 


Chap.  V. 


Plants  of  the  Second  Generation. — The  above  two  lots  of  seeds 
were  placed  on  damp  sand,  and  many  of  the  crossed  seeds 
germinated,  as  on  the  last  occasion,  before  the  self-fertilised,  and 
were  rejected.  Three  or  four  pairs  in  the  same  state  of  germina- 
tion were  planted  on  the  opposite  sides  of  two  pots ;  a  single 
pair  in  a  third  pot ;  and  all  the  remaining  seeds  were  sown  crowded 
in  a  fourth  pot.  When  the  seedlings  were  about  one  and  a  half 
inches  in  height,  they  were  equal  on  both  sides  of  the  three  first 
pots ;  but  in  Pot  IV.,  in  which  they  grew  crowded  and  were 
thus  exposed  to  severe  competition,  the  crossed  were  about  a 
third  taller  than  the  self-fertilised.  In  this  latter  pot,  when 
the  crossed  averaged  5  inches  in  height,  the  self-fertilised  were 
about  4  inches ;  nor  did  they  look  nearly  such  fine  plants. 
In  all  four  pots  the  crossed  plants  flowered  some  days  before 
the  self-fertilised.  When  in  full  flower  the  tallest  plant  on  each 
side  was  measured;  but  before  this  time  the  single  crossed 
plant  in  Pot  III.,  which  was  taller  than  its  antagonist,  had  died 
and  was  not  measured.  So  that  only  the  tallest  plant  on  each 
side  of  three  pots  was  measured,  as  in  the  following  table  :- 

Table  LXIX. 

Lobelia  ramosa  (Second  Generation). 


No.  of  Pot. 

Tallest  Crossed  Plant 
in  each  Pot. 

Tallest  Self-fertilised 
Plant  in  each  Pot. 

I. 

Inches. 
27 1 

Inches. 
18j 

II. 

21 

19| 

IV. 
Crowded. 

21 1 

19 

Total  in  inches. 

70 

57 

The  average  height  of  the  three  tallest  crossed  plants  is  here 
23 '33,  and  that  of  the  three  tallest  self-fertilised  19  inches ;  or  as 
100  to  81.  Besides  this  difference  in  height,  the  crossed  plants 
were  much  more  vigorous  and  more  branched  than  the  self- 
fertilised  plants,  and  it  is  unfortunate  that  they  were  not 
weighed. 


Chap.  V.  LOBELIA   FULGENS.  179 

Lobelia  eulgens. 

This  species  offers  a  somewhat  perplexing  case.  In  the  first 
generation  the  self-fertilised  plants,  though  few  in  number, 
greatly  exceeded  the  crossed  in  height ;  whilst  in  the  second 
generation,  when  the  trial  was  made  on  a  much  larger  scale,  the 
crossed  beat  the  self-fertilised  plants.  As  this  species  is 
generally  propagated  by  off-sets,  some  seedlings  were  first 
raised,  in  order  to  have  distinct  plants.  On  one  of  these  plants 
several  flowers  were  fertilised  with  their  own  pollen ;  and  as  the 
pollen  is  mature  and  shed  long  before  the  stigma  of  the  same 
flower  is  ready  for  fertilisation,  it  was  necessary  to  number  each 
flower  and  keep  its  pollen  in  paper  with  a  corresponding  number. 
By  this  means  well-matured  pollen  was  used  for  self-fertilisation. 
Several  flowers  on  the  same  plant  were  crossed  with  pollen  from 
a  distinct  individual,  and  to  obtain  this  the  conjoined  anthers  of 
young  flowers  were  roughly  squeezed,  and  as  it  is  naturally 
protruded  very  slowly  by  the  growth  of  the  pistil,  it  is  probable 
that  the  pollen  used  by  me  was  hardly  mature,  certainly  less 
mature  than  that  employed  for  self-fertilisation.  I  did  not  at 
the  time  think  of  this  source  of  error,  but  I  now  suspect  that 
the  growth  of  the  crossed  plants  was  thus  injured.  Anyhow  the 
trial  was  not  perfectly  fair.  Opposed  to  the  belief  that  the 
pollen  used  in  crossing  was  not  in  so  good  a  state  as  that  used 
for  self-fertilisation,  is  the  fact  that  a  greater  proportional  number 
of  the  crossed  than  of  the  self-fertilised  flowers  produced  cap- 
sules ;  but  there  was  no  marked  difference  in  the  amount  of  seed 
contained  in  the  capsules  of  the  two  lots.* 

As  the  seeds  obtained  by  the  above  two  methods  would  not 
germinate  when  left  on  bare  sand,  they  were  sown  on  the 
opposite  sides  of  four  pots ;  but  I  succeeded  in  raising  only  a 
single  pair  of  seedlings  of  the  same  age  in  each  pot.  The  self- 
fertilised  seedlings,  when  only  a  few  inches  in  height,  were  in 
most  of  the  pots  taller  than  their  opponents  ;  and  they  flowered 
so  much  earlier  in  all  the  pots,  that  the  height  of  the  flower- 
stems  could  be  fairly  compared  only  in  Pots  I.  and  II. 


*  Gartner  has  shown  that  cer-  but  none  of  the  plants  on  which 

tain  plants  of  Lobelia  fulgens  are  I  experimented,  which  were  kept 

quite  sterile  with  pollen  from  the  in   the   greenhouse,  were  in  this 

same  plant,  though  this  pollen  is  peculiar  condition, 
efficient  on  any  other  individual ; 


180 


LOBELIA  FULGENS. 


Chap.  "V 


Table  LXX. 
Lobelia  fulgens  (First  Generation). 


No.  of  Pot. 

Height  of  Flower- 
stems  on  the  Crossed 
Plants. 

Height  of  Flower- 
stems  on  the  Self-fer- 
tilised Plants. 

I- 

Inches. 
33 

Inches. 
50                ; 

II. 

36  % 

38| 

III. 

21 
Not  in  full  flower. 

43 

IV. 

12 
Not  in  full  flower. 

35f 

The  mean  height  of  the  flower-stems  of  the  two  crossed  plants 
in  Pots  I.  and  II.  is  here  34  "75  inches,  and  that  of  the  two  self- 
fertilised  plants  in  the  same  pots  44*25  inches;  or  as  100  to  127. 
The  self-fertilised  plants  in  Pots  III.  and  IV.  were  in  every 
respect  very  much  finer  than  the  crossed  plants. 

I  was  so  much  surprised  at  this  great  superiority  of  the  self- 
fertilised  over  the  crossed  plants,  that  I  determined  to  try  how 
they  would  behave  in  one  of  the  pots  during  a  second  growth. 
The  two  plants,  therefore,  in  Pot  I.  were  cut  down,  and  repotted 
without  being  disturbed  in  a  much  larger  pot.  In  the  following 
year  the  self-fertilised  plant  showed  even  a  greater  superiority 
than  before;  for  the  two  tallest  flower-stems  produced  by  the 
one  crossed  plant  were  only  29 f  and  30i  inches  in  height, 
whereas  the  two  tallest  stems  on  the  one  self-fertilised  plant 
were  49|  and  49f  inches ;  and  this  gives  a  ratio  of  100  to  167. 
Considering  all  the  evidence,  there  can  be  no  doubt  that  these 
self-fertilised  plants  had  a  great  superiority  over  the  crossed 
plants. 

Grossed  and  self-fertilised  Plants  of  the  Second  Generation. — I 
determined  on  this  occasion  to  avoid  the  error  of  using  pollen  of 
not  quite  equal  maturity  for  crossing  and  self-fertilisation;  so 
that  I  squeezed  pollen  out  of  the  conjoined  anthers  of  young 
flowers  for  both  operations.  Several  flowers  on  the  crossed  plant 
in  Pot  I.  in  Table  LXX.  were  again  crossed  with  pollen  from  a 
distinct  plant.    Several  other  flowers  on  the  self-fertilised  plant 


Chap.  V. 


LOBELIA   FULGENS. 


181 


Table  LXXI. 

Lobelia  fulgens  (Second  Generation). 


No.  of  Pot. 

Crossed  Plants. 
Height  of  Flower- 
stems. 

Self-fertilised  Plants. 
Height  of  Flower- 
stems. 

I. 

Inches. 

27 1 
26 
24  § 
24 1 

Inches. 
32| 
26 1 
25J 
261 

II. 

34 

26  f 
25 1 
26 

361 
28| 
30 1 
32  § 

III. 

40 1 
37 1 
32| 

30 1 
28-| 
23 

IV. 

34 1 
32 1 
29 1 
278 

29| 
28 1 
26 
25  § 

V. 

28 1 
27 
25| 
24f 

29 
24 1 
23§ 
24 

VI. 

33 1 
32 
26 1 
25 

441 
37 1 
37 
35 

VII. 

30  f 
29f 

27 1 
21 

VIII. 

39  jj 
37§ 
36 
36 

23  \ 

23 1 
25 1 
25J 

IX. 

33 1 
25 
25 1 
211 

19§ 
16§ 
19 
18§ 

Total  in  inches. 

1014-00 

921-63 

182  NEMOPHILA  INSIGNIS.  Chap.  V. 

in  the  same  pot  were  again  self-fertilised  with  pollen  from  the 
anthers  of  other  flowers  on  the  same  plant.  Therefore  the  degree 
of  self-fertilisation  was  not  quite  so  close  as  in  the  last  genera- 
tion, in  which  pollen  from  the  same  flower,  kept  in  paper,  was 
used.  These  two  lots  of  seeds  were  thinly  sown  on  opposite 
sides  of  nine  pots ;  and  the  young  seedlings  were  thinned,  an 
equal  number  of  nearly  as  possible  the  same  age  being  left  on 
the  two  sides.  In  the  spring  of  the  following  year  (1870),  when 
the  seedlings  had  grown  to  a  considerable  size,  they  were 
measured  to  the  tips  of  their  leaves  ;  and  the  twenty-three 
crossed  plants  averaged  14  ■  04  inches  in  height,  whilst  the  twenty- 
three  self-fertilised  seedlings  were  13 "  54  inches ;  or  as  100  to  96. 

In  the  summer  of  the  same  year  several  of  these  plants 
flowered,  the  crossed  and  self-fertilised  plants  flowering  almost 
simultaneously,  and  all  the  flower-stems  were  measured.  Those 
produced  by  eleven  of  the  crossed  plants  averaged  30*71  inches, 
and  those  by  nine  of  the  self- fertilised  plants  29*43  inches  in 
height ;  or  as  100  to  96. 

The  plants  in  these  nine  pots,  after  they  had  flowered,  were 
repotted  without  being  disturbed  in  much  larger  pots ;  and  in 
the  following  year,  1871,  all  flowered  freely ;  but  they  had 
grown  into  such  an  entangled  mass,  that  the  separate  plants 
on  each  side  could  no  longer  be  distinguished.  Accordingly 
three  or  four  of  the  tallest  flower-stems  on  each  side  of  each 
pot  were  measured ;  and  the  measurements  in  the  preceding 
table  are,  I  think,  more  trustworthy  than  the  previous  ones, 
from  being  more  numerous,  and  from  the  plants  being  well 
established  and  growing  vigorously. 

The  average  height  of  the  thirty-four  tallest  flower-stems  on 
the  twenty-three  crossed  plants  is  29*82  inches,  and  that  of  the 
same  number  of  flower-stems  on  the  same  number  of  self- 
fertilised  plants  is  27*10  inches;  or  as  100  to  91.  So  that  the 
crossed  plants  now  showed  a  decided  advantage  over  their  self- 
fertilised  opponents. 


XXII.  POLEMONIACE^E.— Nemophila  insignis. 

Twelve  flowers  were  crossed  with  pollen  from  a  distinct  plant, 
but  produced  only  six  capsules,  containing  on  an  average  18*3 
seeds.  Eighteen  flowers  were  fertilised  with  their  own  pollen 
and   produced  ten  capsules,  containing  on  an  average   12*7 


Chap.  V. 


NEMOPHILA   INSIGNIS. 


183 


seeds ;  so  that  the  seeds  per  capsule  were  as  100  to  69.*  The 
crossed  seeds  weighed  a  little  less  than  an  equal  number  of  self- 
fertilised  seeds,  in  the  proportion  of  100  to  105 ;  but  this  was 
clearly  due  to  some  of  the  self-fertilised  capsules  containing  very 
few  seeds,  and  these  were  much  bulkier  than  the  others,  from 
having  been  better  nourished.  A  subsequent  comparison  of  the 
number  of  seeds  in  a  few  capsules  did  not  show  so  great  a 
superiority  on  the  side  of  the  crossed  capsules  as  in  the  present 
case. 

The  seeds  were  placed  on  sand,  and  after  germinating  were 
planted  in  pairs  on  the  opposite  sides  of  five  pots,  which  were 
kept  in  the  greenhouse.  When  the  seedlings  were  from  2  to 
3  inches  in  height,  most  of  the  crossed  had  a  slight  advantage 
over  the  self-fertilised.  The  plants  were  trained  up  sticks,  and 
thus  grew  to  a  considerable  height.  In  four  out  of  the  five 
pots  a  crossed  plant  flowered  before  any  one  of  the  self-fertilised. 

Table  LXXII. 

NemophUa  insignis;  0  means  that  the  plant  died. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches.                           Inches. 
32|                             21§ 

II. 

34| 

23| 

III. 

33£ 

22 1 
29 

19 

173 

IV. 

35f 
33 1 

10| 
27 

V. 

35 
38 
36 
37 f 
32| 

0 
18| 

34 
0 

Total  in  inches. 

399-38 

199-00 

*  Several  species   of   Polemo- 

niacese    are  known  to  be  proter- 

androus,  but  I  did  not  attend  to 

thia  point  in  Nemophila.     Verlot 

9 


says  ('  Des  Variete's,'  1865,  p.  66) 
that  varieties  growing  near  one 
another  spontaneously  intercross. 


184 


NEMOPHILA   INSIGNIS. 


Chap.  V. 


The  plants  were  first  measured  to  the  tips  of  their  leaves,  before 
they  had  flowered  and  when  the  crossed  were  under  a  foot 
in  height.  The  twelve  crossed  plants  averaged  11  "1  inches  in 
height,  whilst  the  twelve  self-fertilised  were  less  than  half  of  this 
height,  viz.,  5  "45 ;  or  as  100  to  49.  Before  the  plants  had  grown 
to  their  full  height,  two  of  the  self-fertilised  died,  and  as  I  feared 
that  this  might  happen  with  others,  they  were  again  measured 
to  the  tops  of  their  stems,  as  shown  in  the  preceding  table. 

The  twelve  crossed  plants  now  averaged  33 '  28,  and  the  ten  self- 
fertilised  19  •  9  inches  in  height,  or  as  100  to  60 ;  so  that  they 
differed  somewhat  less  than  before. 

The  plants  in  Pots  III.  and  V.  were  placed  under  a  net  in  the 
greenhouse,  two  of  the  crossed  plants  in  the  latter  pot  being 
pulled  up  on  account  of  the  death  of  two  of  the  self-fertilised ; 
so  that  altogether  six  crossed  and  six  self-fertilised  plants  were 
left  to  fertilise  themselves  spontaneously.  The  pots  were  rather 
small,  and  the  plants  did  not  produce  many  capsules.  The 
small  size  of  the  self-fertilised  plants  will  largely  account  for 
the  fewness  of  the  capsules  which  they  produced.  The  six  crossed 
plants  bore  105,  and  the  six  self-fertilised  only  30  capsules ;  or  as 
100  to  29. 

The  self-fertilised  seeds  thus  obtained  from  the  crossed  and 
self-fertilised  plants,  after  germinating  on  sand,  were  planted 


Table  LXXIII. 

Nemophila  insignis. 


No.  of  Pot. 

Self-fertilised  Plants 
from  Crossed  Plants. 

Self-fertilised  Plants 

from  Self-fertilised 

Plants. 

I. 

Inches. 

27 
14 

24| 

Inches. 
27 1 
34f 

II. 

23 
32 

III. 

16 

7 

IV. 

16 

Total  in  inches. 

110-13 

147-00 

Chap.  V.  BOKAGO  OFFICINALIS.  185 

on  the  opposite  sides  of  four  small  pots,  and  treated  as  before. 
But  many  of  the  plants  were  unhealthy,  and  their  heights  were  so 
unequal — some  on  both  sides  being  five  times  as  tall  as  the  others 
—that  the  averages  deduced  from  the  measurements  in  the  pre- 
ceding table  are  not  in  the  least  trustworthy.  Nevertheless  I 
have  felt  bound  to  give  them,  as  they  are  opposed  to  my  general 
conclusions. 

The  seven  self-fertilised  plants  from  the  crossed  plants  here 
average  15*73,  and  the  seven  self-fertilised  from  the  self-fertilised 
21  inches  in  height ;  or  as  100  to  133.  Strictly  analogous  experi- 
ments with  Viola  tricolor  and  Lathyrus  odoratus  gave  a  very 
different  result. 

XXIII.  BOKAGINACE^.— Borago  officinalis. 

This  plant  is  frequented  by  a  greater  number  of  bees  than 
almost  any  other  one  which  I  have  observed.  It  is  strongly 
proterandrous  (H.  Miiller,  ' Befruchtung,'  &c,  p.  267),  and  the 
flowers  can  hardly  fail  to  be  cross-fertilised ;  but  should  this 
not  occur,  they  are  capable  of  self-fertilisation  to  a  limited 
extent,  as  some  pollen  long  remains  within  the  anthers,  and  is 
apt  to  fall  on  the  mature  stigma.  In  the  year  1863  I  covered 
up  a  plant,  and  examined  thirty-five  flowers,  of  which  only 
twelve  yielded  any  seeds ;  whereas  of  thirty-five  flowers  on  an 
exposed  plant  growing  close  by,  all  with  the  exception  of  two 
yielded  seeds.  The  covered-up  plant,  however,  produced  alto- 
gether twenty-five  spontaneously  self-fertilised  seeds ;  the  exposed 
plant  producing  fifty-five  seeds,  the  product,  no  doubt,  of  cross- 
fertilisation. 

In  the  year  1868  eighteen  flowers  on  a  protected  plant  were 
crossed  with  pollen  from  a  distinct  plant,  but  only  seven  of  these 
produced  fruit ;  and  I  suspect  that  I  applied  pollen  to  many  of 
the  stigmas  before  they  were  mature.  These  fruits  contained 
on  an  average  2  seeds,  with  a  maximum  in  one  of  three  seeds. 
Twenty-four  spontaneously  self-fertilised  fruits  were  produced 
by  the  same  "plant,  and  these  contained  on  an  average  1 '  2  seeds, 
with  a  maximum  of  two  in  one  fruit.  So  that  the  fruits  from 
the  artificially  crossed  flowers  yielded  seeds  compared  with  those 
from  the  spontaneously  self-fertilised  flowers,  in  the  ratio  of  100 
to  60.  But  the  self-fertilised  seeds,  as  often  occurs  when  few 
are  produced,  were  heavier  than  the  crossed  seeds  in  the  ratio  of 
100  to  90. 


186 


NOlANA   PROSTKATA. 


Chap.  V. 


These  two  lots  of  seeds  were  sown  on  opposite  sides  of  two 
large  pots ;  but  I  succeeded  in  raising  only  four  pairs  of  equal 
age.  When  the  seedlings  on  both  sides  were  about  8  inches 
in  height  they  were  equal.  When  in  full  flower  they  were 
measured,  as  follows : — 

Table  LXXTV. 
Borago  officinalis. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
19 
21 
16| 

Inches. 
13g 
18| 
20 1 

II. 

26§ 

321 

Total  in  inches. 

82-75 

84-75 

The  average  height  of  the  four  crossed  plants  is  here  20 "  68,  and 
that  of  the  four  self-fertilised  21  ■  18  inches ;  or  as  100  to  102. 
The  self-fertilised  plants  thus  exceeded  the  crossed  in  height  by 
a  little ;  but  this  was  entirely  due  to  the  fairness  of  one  of  the 
self-fertilised.  The  crossed  plants  in  both  pots  flowered  before 
the  self-fertilised.  Therefore  I  believe  if  more  plants  had  been 
raised,  the  result  would  have  been  different.  I  regret  that  I  did 
not  attend  to  the  fertility  of  the  two  lots. 


XXIV.  NOLANACE^.— Nolana  prostkata. 

In  some  of  the  flowers  the  stamens  are  considerably  shorter 
than  the  pistil,  in  others  equal  to  it  in  length.  I  suspected, 
therefore,  but  erroneously  as  it  proved,  that  this  plant  was 
dimorphic,  like  Primula,  Linum,  &c,  and  in  the  year  1862  twelve 
plants,  covered  by  a  net  in  the  greenhouse,  were  subjected  to 
trial.  The  spontaneously  self-fertilised  flowers  yielded  64  grains 
weight  of  seeds,  but  the  product  of  fourteen  artificially  crossed 
flowers  is  here  included,  which  falsely  increases  the  weight  of 
the  self-fertilised  seeds.  Nine  uncovered  plants,  the  flowers  of 
which  were  eagerly  visited  by  bees  for  their  pollen  and  were  no 
doubt  intercrossed  by  them,  produced  79  grains  weight  of  seeds : 
therefore  twelve  plants  thus  treated  would  have  yielded  105 


Chap.  V. 


NOLANA   PKOSTRATA. 


187 


grains.  Thus  the  seeds  produced  by  the  flowers  on  an  equal 
number  of  plants,  when  crossed  by  bees,  and  spontaneously  self- 
fertilised  (the  product  of  fourteen  artificially  crossed  flowers 
being,  however,  included  in  the  latter)  were  in  weight  as 
100  to  61. 

In  the  summer  of  1867  the  trial  was  repeated ;  thirty  flowers 
were  crossed  with  pollen  from  a  distinct  plant  and  produced 
twenty-seven  capsules,  each  containing  five  seeds.  Thirty-two 
flowers  were  fertilised  with  their  own  pollen,  and  produced  only 
six  capsules,  each  with  five  seeds.  So  that  the  crossed  and  self- 
fertilised  capsules  contained  the  same  number  of  seeds,  though 
many  more  capsules  were  produced  by  the  cross-fertilised  than 
by  the  self-fertilised  flowers,  in  the  ratio  of  100  to  21. 

An  equal  number  of  seeds  of  both  lots  were  weighed,  and  the 
crossed  seeds  were  to  the  self-fertilised  in  weight  as  100  to  82. 
Therefore  a  cross  increases  the  number  of  capsules  produced  and 
the  weight  of  the  seeds,  but  not  the  number  of  seeds  in  each 
capsule. 

These  two  lots  of  seeds,  after  germinating  on  sand,  were 
planted  on  the  opposite  sides  of  three  pots.  The  seedlings 
when  from  6  to  7  inches  in  height  were  equal.  The  plants 
were  measured  when  fully  grown,  but  their  heights  were  so 
unequal  in  the  several  pots,  that  the  result  cannot  be  fully 
trusted. 

Table  LXXV. 
Nolana  prostrata. 


No.  of  Pot. 

1 
Crossed  Plants.      1  Self-fertilised  Plants. 

I. 

Inches. 
8| 
H 

Inches. 
7j 

II. 

10$ 

18 

14| 

18 

III. 

20§                           22§ 

Total  in  inches. 

63-75 

67-00 

The  five  crossed  plants  average  12*75,  and  the  five  self- 
fertilised  13 "4  inches  in  height;  or  as  100  to  105. 


L88  PETUNIA   VIOLACEA.  Chap.  VI. 


CHAPTER  VI. 

SOLANACE^!,    PRIMULACEiE,   POLYGONE^!,  ETC. 

Petunia  violacea,  crossed  and  self-fertilised  plants  compared  for  four 
generations — Effects  of  a  cross  with  a  fresh  stock  —Uniform  colour 
of  the  flowers  on  the  self-fertilised  plants  of  the  fourth  generation 
— Nicotiana  tab.icum,  crossed  and  self-fertilised  plants  of  equal 
height — Great  effects  of  a  cross  with  a  distinct  sub-variety  on  the 
height,  but  not  on  the  fertility,  of  the  offspring — Cyclamen  per- 
sicum,  crossed  seedlings  greatly  superior  to  the  self-fertilised — 
Anagallis  collina — Primula  veris — Equal-otyled  variety  of  Primula 
veris,  fertility  of,  greatly  increased  by  a  cross  with  a  fresh  stock — 
Fagopyrum  esculentum — Beta  vulgaris — Canna  warscewiczi,  crossed 
and  self-fertilised  plants  of  equal  height — Zea  mays — Phalaris 
canadensis. 

XXV.  SOLANACE.E.— Petunia  violacea. 
Dingy  purple  variety. 

The  flowers  of  this  plant  are  so  seldom  visited  during  the  day 
by  insects  in  this  country,  that  I  have  never  seen  an  instance ; 
but  my  gardener,  on  whom  I  can  rely,  once  saw  some  humble- 
bees  at  work.  Mr.  Meehan  says,*  that  in  the  United  States 
bees  bore  through  the  corolla  for  the  nectar,  and  adds  that  their 
"  fertilisation  is  carried  on  by  night-moths." 

In  France  M.  Naudin,  after  castrating  a  large  number  of  flowers 
whilst  in  bud,  left  them  exposed  to  the  visits  of  insects,  and 
about  a  quarter  produced  capsules  ;f  but  I  am  convinced  that 
a  much  larger  proportion  of  flowers  in  my  garden  are  cross- 
fertilised  by  insects,  for  protected  flowers  with  their  own  pollen 
placed  on  the  stigma  never  yielded  nearly  a  full  complement  of 
seed ;  whilst  those  left  uncovered  produced  fine  capsules,  showing 
that  pollen  from  other  plants  must  have  been  brought  to  them, 
probably  by  moths.  Plants  growing  vigorously  and  flowering  in 
pots  in  the  green-house,  never  yielded  a  single  capsule ;   and 


*  '  Proc.  Acad.  Nat.  Sc.  of  Phil-  f  'Annales  des   Sc.  Nat.'  4tb 

adelphia,'  Aug.  2nd.  1870,  p.  90.         series,  Bot.  torn,  ix,  cah.  5. 


Chap.  VI.   CEOSSED   AND   SELF-FEKTILISED   PLANTS.      189 

this  may  be  attributed,  at  least  in  chief  part,  to  the  exclusion 
of  moths. 

Six  flowers  on  a  plant  covered  by  a  net  were  crossed  with 
pollen  from  a  distinct  plant  and  produced  six  capsules,  containing 
by  weight  4  "44  grains  of  seed.  Six  other  flowers  were  fertilised 
with  their  own  pollen  and  produced  only  three  capsules,  con- 
taining only  1  •  49  grains  weight  of  seed.  From  this  it  follows 
that  an  equal  number  of  crossed  and  self- fertilised  capsules  would 
have  contained  seeds  by  weight  as  100  to  67.  I  should  not  have 
thought  the  proportional  contents  of  so  few  capsules  worth 
giving,  had  not  nearly  the  same  result  been  confirmed  by  several 
subsequent  trials. 

Seeds  of  the  two  lots  were  placed  on  sand,  and  many  of  the 
self-fertilised  seeds  germinated  before  the  crossed,  and  were 
rejected.  Several  pairs  in  an  equal  state  of  germination  were 
planted  on  the  opposite  sides  of  Pots  I.  and  II. ;  but  only  the 
tallest  plant  on  each  side  was  measured.  Seeds  were  also  sown 
thickly  on  the  two  sides  of  a  large  pot  (III.),  the  seedlings  being 
afterwards  thinned,  so  that  an  equal  number  was  left  on  each 
side ;  the  three  tallest  on  each  side  being  measured.  The  pots 
were  kept  in  the  greenhouse,  and  the  plants  were  trained  up 
sticks.  For  some  time  the  young  crossed  plants  had  no  ad- 
vantage in  height  over  the  self-fertilised;  but  their  leaves 
were  larger.  When  fully  grown  and  in  flower  the  plants  were 
measured,  as  follows  : — 

Table  LXXVI. 
Petunia  violucea  (First  Generation). 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
30 

Inches. 
20 1 

II. 

34 1 

27^ 

III. 

34 
30 1 
25 

154 

28| 

27 1 
26 

Total  in  inches. 

130 

The  five  tallest  crossed  plants  here  average  30 "  8,  and  the  five 
tallest  self-fertilised  26  inches  in  height,  or  as  100  to  84. 


190 


PETUNIA  VIOLACEA. 


Chap.  VI. 


Three  capsules  were  obtained  by  crossing  flowers  on  the 
above  crossed  plants,  and  three  other  capsules  by  again  self- 
fertilising  flowers  on  the  self-fertilised  plants.  One  of  the  latter 
capsules  appeared  as  fine  as  any  one  of  the  crossed  capsules ; 
but  the  other  two  contained  many  imperfect  seeds.  From  these' 
two  lots  of  seeds  the  plants  of  the  following  generation  were 
raised. 

Crossed  and  self -fertilised  Plants  of  the  Second  Generation. — As  in 
the  last  generation,  many  of  the  self-fertilised  seeds  germinated 
before  the  crossed. 

Seeds  in  an  equal  state  of  germination  were  planted  on  the 
opposite  sides  of  three  pots.  The  crossed  seedlings  soon  greatly 
exceeded  in  height  the  self-fertilised.  In  Pot  L,  when  the  tallest 
crossed  plant  was  IO5  inches  high,  the  tallest  self-fertilised  was 
only  3  s  inches ;  in  Pot  II.  the  excess  in  height  of  the  crossed  was 
not  quite  so  great.  The  plants  were  treated  as  in  the  last  gene- 
ration, and  when  fully  grown  measured  as  before.  In  Pot  III. 
both  the  crossed  plants  were  killed  at  an  early  age  by  some 
animal,  so  that  the  self-fertilised  had  no  competitors.  Neverthe- 
less these  two  self-fertilised  plants  were  measured,  and  are  in- 
cluded in  the  following  table.  The  crossed  plants  flowered  long 
before  their  self-fertilised  opponents  in  Pots  I.  and  II.,  and  before 
those  growing  separately  in  Pot  III. 

Table  LXXVII 

Petunia  violacea  {Second  Generation). 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
57  § 
36 1 

Inches. 

8          ; 

II. 

44f 
24 

33| 
28 

III. 

0 
0 

46  § 

28|            ! 

Total  in  inches.                162-0 

157-5 

The  four  crossed  plants  average  40*5,  and  the  six  self-fer- 
tilised 26  •  25  inches  in  height ;  or  as  100  to  65.  But  this  great 
inequality  is  in  part  accidental,  owing  to  some  of  the  self- 


Chap.  VI.    CROSSED    AND    SELF-FERTILISED   PLANTS.      191 


fertilised  plants  being  very  short,  and  to  one  of  the  crossed  being 
very  tall. 

Twelve  flowers  on  these  crossed  plants  were  again  crossed,  and 
eleven  capsules  were  produced ;  of  these,  five  were  poor  and  six 
good;  the  latter  contained  by  weight  3*75  grains  of  seeds. 
Twelve  flowers  on  the  self-fertilised  plants  were  again  fertilised 
with  their  own  pollen  and  produced  no  less  than  twelve  capsules, 
and  the  six  finest  of  these  contained  by  weight  2  ■  57  grains  of 
seeds.  It  should  however  be  observed  that  these  latter  capsules 
were  produced  by  the  plants  in  Pot  III.,  which  were  not  exposed 
to  any  competition.  The  seeds  in  the  six  fine  crossed  capsules 
to  those  in  the  six  finest  self-fertilised  capsules  were  in  weight 
as  100  to  68.  From  these  seeds  the  plants  of  the  next  generation 
were  raised. 

Crossed  and  sdf-fertilised  Plants  of  the  Third  Generation. — The 
above  seeds  were  placed  on  sand,  and  after  germinating  were 
planted  in  pairs  on  the  opposite  sides  of  four  pots ;  and  all  the 
remaining  seeds  were  thickly  sown  on  the  two  sides  of  a  fifth  large 
pot.  The  result  was  surprising,  for  the  self-fertilised  seedlings 
very  early  in  life  beat  the  crossed,  and  at  one  time  were  nearly 
double  their  height.  At  first  the  case  appeared  like  that  of 
Mimulus,  in  which  after  the  third  generation  a  fall  and  highly 
self-fertile  variety  appeared.  But  as  in  the  two  succeeding 
generations  the  crossed  plants  resumed  their  former  superiority 
over  the  self-fertilised,  the  case  must  be  looked  at  as  an  anomaly. 
The  sole  conjecture  which  I  can  form  is  that  the  crossed  seeds 

Table  LXXVIII. 

Petunia  violacea  {Third  Generation ;  plants  very  young). 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
1  * 

1 

Inches. 

°3 

4.4 

II. 

5| 

81 
61 

III. 

4 

H 

IV. 

i  * 

°5 

Total  in  inches. 

19-63 

36-50 

L92 


PETUNIA   VIOLACEA. 


Chap.  VI. 


had  not  been  sufficiently  ripened,  and  thus  proauced  weakly 
plants,  as  occurred  with  Iberis.  When  the  crossed  plants  were 
between  3  and  4  inches  in  height,  the  six  finest  in  four  of  the 
pots  were  measured  to  the  summits  of  their  stems,  and  at  the 
same  time  the  six  finest  of  the  self-fertilised  plants.  The 
measurements  are  given  in  the  preceding  table  (LXXVIII ),  and 
it  may  be  here  seen  that  all  the  self-fertilised  plants  exceed  their 
opponents  in  height,  whereas  when  subsequently  measured  the 
excess  of  the  self-fertilised  depended  chiefly  on  the  unusual  tall- 
ness  of  two  of  the  plants  in  Pot  II.  The  crossed  plants  here 
average  3  ■  27,  and  the  self-fertilised  6  ■  08  inches  in  height ;  or 
as  100  to  186. 

When  fully  grown  they  were  again  measured,  as  follows : — 


Table  LXXIX. 

Petunia  violacea  (Third  Generation;  plants  fully  grown). 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
41 1 
48 
36 

Inches. 
40 1 
39 
48 

II. 

36 
21 
36 1 

47 
80 1 

86 1 

III. 

52 

46 

IV. 

57 

43§             | 

Total  in  inches. 

327-75 

431-00 

The  eight  crossed  plants  now  averaged  40 '  96,  and  the  eight 
self-fertilised  plants  53 '  87  inches  in  height,  or  as  100  to  131 ;  and 
tbis  excess  chiefly  depended,  as  already  stated,  on  the  unusual 
tallness  of  two  of  the  self-fertilised  plants  in  Pot  II.  The  self- 
fertilised  had  therefore  lost  some  of  their  former  great  superiority 
over  the  crossed  plants.  In  three  of  the  pots  the  self-fertilised 
plants  flowered  first;  but  in  Pot  III.  at  the  same  time  with 
the  crossed. 

The  case  is  rendered  the  more  strange,  because  the  crossed 
plants  in  the  fifth  pot  (not  included  in  the  two  last  tables),  in 


Chap.  VI.   CROSSED    AND   SELF-FERTILISED   PLANTS.      193 

which  all  the  remaining  seeds  had  been  thickly  sown,  were  from 
the  first  finer  plants  than  the  self-fertilised,  and  had  larger 
leaves.  At  the  period  when  the  two  tallest  crossed  plants  in 
this  pot  were  6|  and  4|  inches  high,  the  two  tallest  self-fertilised 
were  only  4  inches.  When  the  two  crossed  plants  were  12  and 
10  inches  high,  the  two  self-fertilised  were  only  8  inches.  These 
latter  plants,  as  well  as  many  others  on  the  same  side  of  this  pot 
never  grew  any  higher,  whereas  several  of  the  crossed  plants 
grew  to  the  height  of  two  feet!  On  account  of  this  great 
superiority  of  the  crossed  plants,  the  plants  on  neither  side  of 
this  pot  have  been  included  in  the  two  last  tables. 

Thirty  flowers  on  the  crossed  plants  in  Pots  I.  and  IV.  (Table 
LXXIX.)  were  again  crossed,  and  produced  seventeen  capsules. 
Thirty  flowers  on  the  self-fertilised  plants  in  the  same  two  pots 
were  again  self-fertilised,  but  produced  only  seven  capsules. 
The  contents  of  each  capsule  of  both  lots  were  placed  in  separate 
watch-glasses,  and  the  seeds  from  the  crossed  appeared  to  the 
eye  to  be  at  least  double  the  number  of  those  from  the  self- 
fertilised  capsules. 

In  order  to  ascertain  whether  the  fertility  of  the  self-fertilised 
plants  had  been  lessened  by  the  plants  having  been  self-ferti- 
lised for  the  three  previous  generations,  thirty  flowers  on  the 
crossed  plants  were  fertilised  with  their  own  pollen.  These 
yielded  only  five  capsules,  and  their  seeds  being  placed  in 
separate  watch-glasses  did  not  seem  more  numerous  than  those 
from  the  capsules  on  the  self-fertilised  plants  self-fertilised  for 
the  fourth  time.  So  that  as  far  as  can  be  judged  from  so  few 
capsules,  the  self-fertility  of  the  self-fertilised  plants  had  not 
decreased  in  comparison  with  that  of  the  plants  which  had 
been  intercrossed  during  the  three  previous  generations.  It 
should,  however,  be  remembered  that  both  lots  of  plants 
had  been  subjected  in  each  generation  to  almost  exactly  similar 
conditions. 

Seeds  from  the  crossed  plants  again  crossed,  and  from  the  self- 
fertilised  again  self-fertilised,  produced  by  the  plants  in  Pot  I. 
(Table  LXXIX.),  in  which  the  three  self-fertilised  plants  were 
on  an  average  only  a  little  taller  than  the  crossed,  were  used  in 
the  following  experiment.  They  were  kept  separate  from  two 
similar  lots  of  seeds  produced  by  the  two  plants  in  Pot  IV.  in 
the  same  table,  in  which  the  crossed  plant  was  much  taller  than 
its  self-fertilised  opponent. 

Crossed    and   self-fertilised   Plants   of  the   Fourth    Generation 


194 


PETUNIA   VIOLACEA. 


Chap.  VI. 


(raised  from  the  Flcmts  in  Pot  J.,  Table  LXXIX.). — Crossed  and 
self-fertilised  seeds  from  plants  of  the  last  generation  in  Pot  L, 
in  Table  LXXIX.,  were  placed  on  sand,  and  after  germinating, 
were  planted  in  pairs  on  the  opposite  sides  of  four  pots.  The 
seedlings  when  in  full  flower  were  measured  to  the  base  of  the 
calyx.  The  remaining  seeds  were  sown  crowded  on  the  two 
sides  of  Pot  V. ;  and  the  four  tallest  plants  on  each  side  of  this 
pot  were  measured  in  the  same  manner. 


Table  LXXX. 

Petunia  violacea  (Fourth  Generation ;  raised  from  Plants  of  the 

Third  Generation  in  Pot  L,  Table  LXXIX.). 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
29§ 
36 1 
49 

Inches. 
30 1 
34  § 
311 

II. 

33 1 
37 1 
56 1 

31 1 
38  f 
38j 

IIL 

46 
67  § 
54§ 

45J 

45 

23§ 

IV. 

51? 

51? 

34 
0 

V. 

Crowded  plants. 

49 1 
46§ 
40 
53 

22  § 
24  § 
24  f 
30 

Total  in  inches.    \            701-88         |             453-50 

The  fifteen  crossed  plants  average  46-79,  and  the  fourteen 
(one  having  died)  self-fertilised  plants  32 '  39  inches  in  height ;  or 
as  100  to  69.  So  that  the  crossed  plants  in  this  generation  had 
recovered  their  wonted  superiority  over  the  self-fertilised  plants  5 
though  the  parents  of  the  latter  in  Pot  I.,  Table  LXXIX.,  were  a 
little  taller  than  their  crossed  opponents. 

Crossed  and    self-fertilised   Plants    of  the    Fourth    Generation 


Chap.  VI    CROSSED   AND   SELF-FERTILISED   PLANTS.      195 


(raised  from,  the  Plants  in  Pot  7  V.,  in  Table  LXXIX.). — Two 
similar  lots  of  seeds,  obtained  from  the  plants  in  Pot  IV.  in 
Table  LXXIX.,  in  which  the  single  crossed  plant  was  at 
first  shorter,  but  ultimately  much  taller  than  its  self-fertilised 
opponent,  were  treated  in  every  way  like  their  brethren  of  the 
same  generation  in  the  last  experiment.  We  have  in  the  follow- 
ing Table  LXXXI.  the  measurements  of  the  present  plants 
Although  the  crossed  plants  greatly  exceeded  in  height  the  self- 
fertilised  ;  yet  in  three  out  of  the  five  pots  a  self-fertilised  plant 
flowered  before  any  one  of  the  crossed ;  in  a  fourth  pot  simul- 
taneously ;  and  in  a  fifth  (viz.,  Pot  II.)  a  crossed  plant  flowered 
first. 

Table  LXXXI. 

Petunia  violacea  (Fourth  Generation ;  raised  from  Plants  of  the 
Third  Generation  in  Pot  IV.,  Table  LXXIX.). 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

Inches. 
30  § 
28 

I. 

Inches. 
46 
46 

II. 

50  f 
40 1 
37 1 

25 

31| 

22| 

III. 

54 1 
61* 

45 

22| 
26 1 
32 

IV. 

30 
29J 

28j 

26 

V. 

Crowded  plants. 

37 1 
63 
41  § 

40 1 
18| 

"  j 

Total  in  inches. 

581-63 

349-36 

The  thirteen  crossed  plants  here  average  44-74,  and  the 
thirteen  self-fertilised  plants  26 '  87  inches  in  height ;  or  as  100 
to  60.  The  crossed  parents  of  these  plants  were  much  taller, 
relatively  to  the  self-fertilised  parents,  than  in  the  last  case ;  and 
apparently  they  transmitted  some  of  this  superiority  to  their 


196  PETUNIA   VIOLACEA.  Chap.  VI. 

crossed  offspring.  It  is  unfortunate  that  I  did  not  turn  these 
plants  out  of  doors,  so  as  to  observe  their  relative  fertility,  for  1 
compared  the  pollen  from  some  of  the  crossed  and  self-fertilised 
plants  in  Pot  I.,  Table  LXXXL,  and  there  was  a  marked  dif- 
ference in  its  state ;  that  of  the  crossed  plants  contained  hardly 
any  bad  and  empty  grains,  whilst  such  abounded  in  the  pollen 
of  the  self-ferfilised  plants. 

The  Effects  of  a  Cross  with  a  fnsh  Stock.— I  procured  from  a 
garden  in  Westerham,  whence  my  plants  originally  came,  a 
fresh  plant  differing  in  no  respect  from  mine  except  in  the 
colour  of  the  flowers,  which  was  a  fine  purple.  But  this  plant 
must  have  been  exposed  during  at  least  four  generations  to  very 
different  conditions  from  those  to  which  my  plants  had  been 
subjected,  as  these  had  been  grown  in  pots  in  the  green- 
house. Eight  flowers  on  the  self-fertilised  plants  in  Table 
LXXXL,  of  the  last  or  fourth  self-fertilised  generation,  were 
fertilised  with  pollen  from  this  fresh  stock ;  all  eight  produced 
capsules  containing  together  by  weight  5*01  grains  of  seeds. 
The  plants  raised  from  these  seeds  may  be  called  the  Westerham- 
crossed. 

Eight  flowers  on  the  crossed  plants  of  the  last  or  fourth  genera- 
tion in  Table  LXXXL  were  again  crossed  with  pollen  from  one 
of  the  other  crossed  plants,  and  produced  five  capsules,  contain- 
ing by  weight  2-07  grains  of  seeds.  The  plants  raised  from 
these  seeds  may  be  called  the  intercrossed ;  and  these  form  the 
fifth  intercrossed  generation. 

Eight  flowers  on  the  self-fertilised  plants  of  the  same  genera-  ' 
tion  in  Table  LXXXL  were  again  self-fertilised,  and  produced 
seven  capsules,  containing  by  weight  2*1  grains  of  seeds.  The 
self-fertilised  plants  raised  from  these  seeds  form  the  fifth  self- 
fertilised  generation.  These  latter  plants  and  the  intercrossed 
are  comparable  in  all  respects  with  the  crossed  and  self-fertilised 
plants  of  the  four  previous  generations. 

From  the  foregoing  data  it  is  easy  to  calculate  that, 

Gr.  Weight 

of  Seed. 

Ten  Westerham-crossed  capsules  would  have  contained    6  ■  26 

Ten  intercrossed  capsules  would  have  contained  .         .     4*14 

Ten  self-fertilised  capsules  would  have  contained         .     3 '00 

We  thus  get  the  following  ratios : — 


Chap.  VI.  CROSS   WITH  A   FRESH   STOCK.  197 

Seeds  from  the  Westerham-crossed  capsules  to 
those  from  the  capsules  of  the  fifth  self-fer- 
tilised generation,  in  weight,         .         .         .as  100  to  48 

Seeds  from  the  Westerham-crossed  capsules  to 
those  from  the  capsules  of  the  fifth  intercrossed 
generation,  ......     as  100  to  66 

Seeds  from  the  intercrossed  to  those  from  the 
self-fertilised  capsules,  .         .         .         .as  100  to  72 

So  that  a  cross  with  pollen  from  a  fresh  stock  greatly  increased 
the  productiveness  of  the  flowers  on  plants  which  had  been  self- 
fertilised  for  the  four  previous  generations,  in  comparison  not 
only  with  the  flowers  on  the  same  plants  self-fertilised  for  the  fifth 
time,  but  with  the  flowers  on  the  crossed  plants  crossed  with 
pollen  from  another  plant  of  the  same  old  stock  for  the  fifth 
time. 

These  three  lots  of  seeds  were  placed  on  sand,  and  were 
planted  in  an  equal  state  of  germination  in  seven  pots,  each  made 
tripartite  by  three  superficial  partitions.  Some  of  the  remaining 
seeds,  whether  or  not  in  a  state  of  germination,  were  thickly 
sown  in  an  eighth  pot.  The  pots  were  kept  in  the  greenhouse, 
and  the  plants  trained  up  sticks.  They  were  first  measured  to 
the  tops  of  their  stems  when  coming  into  flower ;  and  the  twenty- 
two  Westerhaui-crossed  plants  then  averaged  25*51  inches;  the 
twenty-three  intercrossed  plants  30  "38;  and  the  twenty-three 
self-fertilised  plants  23  ■  40  inches  in  height.  We  thus  get  the 
following  ratios : — 

The  Westerham-crossed  plants  in  height  to  the 
self-fertilised       .         .  .         .         .as  100  to    91 

The  Westerham-crossed  plants  in  height  to  the 
intercrossed         .         .         .         .         .         .as  100  to  119 

The  intercrossed  plants  in  height  to  the  self- 
fertilised    as  100  to   77 

These  plants  were  again  measured  when  their  growth  appeared 
on  a  casual  inspection  to  be  complete.  But  in  this  I  was  mis- 
taken, for  after  cutting  them  down,  I  found  that  the  summits 
of  the  stems  of  the  Westerham-crossed  plants  were  still  growing 
vigorously ;  whilst  the  intercrossed  had  almost,  and  the  self- 
fertilised  had  quite  completed  their  growth.  Therefore  I  do 
not  doubt,  if  the  three  lots  had  been  left  to  grow  for  another 
month,  that  the  ratios  would  have  been  somewhat  different 


198 


PETUNIA   VIOLACEA. 


Chap.  VL 


from  those  deduced  from  the  measurements  in  the  following 
table : — 

Table  LXXXn. 

Petunia  violacea. 


No.  of  Pot. 

Westerham-crossed  t„*™™x™„j  t>i t„  < 

P]     .    rtw«m  q  if    Intercrossed  Plants 

ssSES  °asssr,«sssai8f 

I. 

Inches. 

24 
51| 

Inches. 
571 
64 
58  § 

Inches. 
43 1 
56 1 
31 1 

II. 

48 1 
54f 
58 1 

591 
581 
53 

41 1 

41! 
181 

III. 

62 
53 ? 
62f 

52f                       46f 
54 1                       45 
61g           j             19J 

IV. 

44  £ 
49 1 

581 
651 
59 1 

37 1 
331 
321 

V. 

43 1 
53 1 
53f 

35 1                       41 1 
34|                       26 | 

54|                         0 

VI. 

37  i 

61 

0 

56 
63| 

571 

46 1 

29 1 

1*1 

VII. 

59  f 
43 1 
50 1 

51 

49 1 
0 

1 

43 

12? 

0 

VIII. 

Crowded. 

37^ 
37§ 

38|                      21§ 

44 g                       14g 

i 

Total  in  inches. 

1051-25 

1190-50                 697-88 

The  twenty-one  "Westerham-crossed  plants  now  averaged  50 "  05 
inches;  the  twenty-two  intercrossed  plants,  54 "11  inches;  and 
the  twenty-one  self-fertilised  plants,  33  "23  inches  in  height.  We 
thus  get  the  following  ratios:  — 


Chap.  VI.  CEOSS   WITH   A   FRESH   STOCK.  199 

The  Westerham-crossed  plants  in  height  to  the 
self-fertilised as  100  to    66 

The  Westerham-crossed  plants  in  height  to  the 
intercrossed        .         .         .         .         .         .as  100  to  108 

The  intercrossed  plants  in  height  to  the  self- 
fertilised     as  100  to   61 

We  here  see  that  the  Westerham-crossed  (the  offspring  of 
plants  self-fertilised  for  four  generations  and  then  crossed  with  a 
fresh  stock)  have  gained  greatly  in  height,  since  they  were  first 
measured,  relatively  to  the  plants  self-fertilised  for  five  genera- 
tions. They  were  then  as  100  to  91,  and  now  as  100  to  66  in 
height.  The  intercrossed  plants  (i.e.,  those  which  had  been  in- 
tercrossed for  the  last  five  generations)  likewise  exceed  in 
height  the  self-fertilised  plants,  as  occurred  in  all  the  previous 
generations  with  the  exception  of  the  abnormal  plants  of  the 
third  generation.  On  the  other  hand,  the  Westerham-crossed 
plants  are  exceeded  in  height  by  the  intercrossed ;  and  this  is  a 
surprising  fact,  judging  from  most  of  the  other  strictly  analogous 
cases.  But  as  the  Westerham-crossed  plants  were  still  growing 
vigorously,  while  the  intercrossed  had  almost  ceased  to  grow, 
there  can  hardly  be  a  doubt  that  if  left  to  grow  for  another 
month  they  would  have  beaten  the  intercrossed  in  height.  That 
they  were  gaining  on  them  is  clear,  as  when  measured  before  they 
were  as  100  to  119,  and  now  as  only  100  to  108  in  height.  The 
Westerham-crossed  plants  had  also  leaves  of  a  darker  green,  and 
looked  altogether  more  vigorous  than  the  intercrossed  ;  and  what 
is  much  more  important,  they  produced,  as  we  shall  presently 
see,  much  heavier  seed-capsules.  So  that  in  fact  the  offspring 
from  the  self-fertilised  plants  of  the  fourth  generation  crossed  by 
a  fresh  stock  were  superior  to  the  intercrossed,  as  well  as  to  the 
self-fertilised  plants  of  the  fifth  generation — of  which  latter  fact 
there  could  not  be  the  least  doubt. 

These  three  lots  of  plants  were  cut  down  close  to  the  ground 
and  weighed.  The  twenty-one  Westerham-crossed  plants  weighed 
32  ounces  ;  the  twenty-two  intercrossed  plants,  34  ounces,  and  the 
twenty-one  self-fertilised  plants  li  ounces.  The  following  ratios 
are  calculated  for  an  equal  number  of  plants  of  each  kind.  But 
as  the  self-fertilised  plants  were  just  beginning  to  wither,  their 
relative  weight  is  here  slightly  too  small ;  and  as  the  Westerham- 
crossed  were  still  growing  vigorously,  their  relative  weight 
with  time  allowed  would  no  doubt  have  greatly  increased. 


200 


PETUNIA   VIOLACEA. 


Chap.  VI. 


The  Westerham-crossed  plants  in  weight  to 
the  self-fertilised as  100  to    22 

The  Westerham-crossed  plants  in  weight  to 
the  intercrossed       .         .         .         .         .as  100  to  101 

The  intercrossed  plants  in  weight  to  the  self- 
fertilised         as  100  to   22-3 


We  here  see,  judging  by  weight  instead  of  as  before  by  height, 
that  the  Westerham-crossed  and  the  intercrossed  have  an 
immense  advantage  over  the  self-fertilised.  The  Westerham- 
crossed  are  inferior  to  the  intercrossed  by  a  mere  trifle ;  but  it  is 
almost  certain  that  if  they  had  been  allowed  to  go  on  growing  for 
another  month,  the  former  would  have  completely  beaten  the 
latter. 

As  I  had  an  abundance  of  seeds  of  the  same  three  lots,  from 
which  the  foregoing  plants  had  been  raised,  these  were  sown  in 
three  long  parallel  and  adjoining  rows  in  the  open  ground,  so  as  to 
ascertain  whether  under  these  circumstances  the  results  would  be 
nearly  the  same  as  before.  Late  in  the  autumn  (Nov.  13)  the  ten 
tallest  plants  were  carefully  selected  out  of  each  row,  and  their 
heights  measured,  with  the  following  result : — 


Table  LXXXHI. 

Petunia  violacea  (plants  growing  in  the  open  ground'). 


Westerham-crossed 
Plants  (from  Self- 
fertilised  Plants  of  the 
Fourth  Generation 
crossed  by  a  fresh 
Stock). 

Intercrossed  Plants 
(Plants  of  one  and  the 
same  Stock  inter- 
crossed for  Five 
Generations). 

Self-fertilised  Plants 
(Self-fertilised  for 
Five  Generations). 

Inches. 
34 1 
361 
35 1 
32J 
37 
36 1 
40 1 
37 1 
38 1 
38 1 

Inches. 
38 
36§ 
39 1 
37 
36 
41 1 
37 1 
40 

4.1  2 

36 

Inches. 
27 1 
23 
25 
24 1 
22 1 
23 1 

21f 
23,£ 
21 1 
21| 

366-76 

382-76 

233-13         J 

Chap.  VI.  CROSS   WITH   A   FRESH   STOCK.  201 

The  ten  Westerham-crossed  plants  here  average  36  ■  67  inches 
in  height ;  the  ten  intercrossed  plants,  38  ■  27  inches ;  and  the  ten 
self-fertilised,  23*31  inches.  These  three  lots  of  plants  were  also 
weighed ;  the  Westerham-crossed  plants  weighed  28  ounces ;  the 
intercrossed,  41  ounces  j  and  the  self-fertilised,  14*75  ounces. 
We  thus  get  the  following  ratios  : — 

The  Westerham-crossed  plants  in  height  to  the 
self-fertilised as  100  to    63 

The  Westerham-crossed  plants  in  weight  to  the 
self-fertilised    ......     as  100  to    53 

The  Westerham-crossed  plants  in  height  to  the 
intercrossed       ......     as  100  to  104 

The  Westerham-crossed  plants  in  weight  to  the 
intercrossed      .         .         .         .         .         .as  100  to  146 

The  intercrossed  plants  in  height  to  the  self- 
fertilised  as  100  to    61 

The  intercrossed  plants  in  weight  to  the  self- 
fertilised  as  100  to    36 

Here  the  relative  heights  of  the  three  lots  are  nearly  the  same 
(within  three  or  four  per  cent.)  as  with  the  plants  in  the  pots. 
In  weight  there  is  a  much  greater  difference :  the  Westerham- 
crossed  exceed  the  self-fertilised  by  much  less  than  they  did 
before ;  but  the  self-fertilised  plants  in  the  pots  had  become 
slightly  withered,  as  before  stated,  and  were  in  consequence 
unfairly  light.  The  Westerham-crossed  plants  are  here  inferior 
in  weight  to  the  intercrossed  plants  in  a  much  higher  degree 
than  in  the  pots ;  and  this  appeared  due  to  their  being  much 
less  branched,  owing  to  their  having  germinated  in  greater 
numbers  and  consequently  being  much  crowded.  Their  leaves 
were  of  a  brighter  green  than  those  of  the  intercrossed  and 
self-fertilised  plants. 

Relative  Fertility  of  the  Three  Lots  of  Plants. — None  of  the  plants 
in  pots  in  the  greenhouse  ever  produced  a  capsule ;  and  this  may 
be  attributed  in  chief  part  to  the  exclusion  of  moths.  There- 
fore the  fertility  of  the  three  lots  could  be  judged  of  only  by  that 
of  the  plants  growing  out  of  doors,  which  from  being  left 
uncovered  were  probably  cross-fertilised.  The  plants  in  the 
three  rows  were  exactly  of  the  same  age  and  had  been  subjected 
to  closely  similar  conditions,  so  that  any  difference  in  their  fer- 
tility must  be  attributed  to  their  different  origin ;  namely,  to  the 


202  TETUNIA  VIOLACEA.  Chap.  VI. 

one  lot  being  derived  from  plants  self-fertilised  for  four  genera- 
tions and  then  crossed  with  a  fresh  stock ;  to  the  second  lot  being 
derived  from  plants  of  the  same  old  stock  intercrossed  for  five 
generations ;  and  to  the  third  lot  being  derived  from  plants  self- 
fertilised  for  five  generations.  All  the  capsules,  some  nearly 
mature  and  some  only  half-grown,  were  gathered,  counted,  and 
weighed  from  the  ten  finest  plants  in  each  of  the  three  rows,  of 
which  the  measurements  and  weights  have  already  been  given. 
The  intercrossed  plants,  as  we  have  seen,  were  taller  and  con- 
siderably heavier  than  the  plants  of  the  other  two  lots,  and  they 
produced  a  greater  number  of  capsules  than  did  even  the 
Westerham-crossed  plants ;  and  this  may  be  attributed  to  the 
latter  having  grown  more  crowded  and  being  in  consequence  less 
branched.  Therefore  the  average  weight  of  an  equal  number  of 
capsules  from  each  lot  of  plants  seems  to  be  the  fairest  standard 
of  comparison,  as  their  weights  will  have  been  determined  chiefly 
by  the  number  of  the  included  seeds.  As  the  intercrossed  plants 
were  taller  and  heavier  than  the  plants  of  the  other  two  lots,  it 
might  have  been  expected  that  they  would  have  produced  the  finest 
or  heaviest  capsules ;  but  this  was  very  far  from  being  the  case. 

The  ten  tallest  Westerham-crossed  plants  produced  111  ripe 
and  unripe  capsules,  weighing  121  ■  2  grains.  Therefore  100  of 
such  capsules  would  have  weighed  109  ■  18  grains. 

The  ten  tallest  intercrossed  plants  produced  129  capsules, 
weighing  76  "45  grains.  Therefore  100  of  these  capsules  would 
have  weighed  59  ■  26  grains. 

The  ten  tallest  self-fertilised  plants  produced  only  44  capsules, 
weighing  22 '  35  grains.  Therefore  100  of  these  capsules  would 
have  weighed  50  *79  grains. 

From  these  data  we  get  the  following  ratios  for  the  fertility  of 
the  three  lots,  as  deduced  from  the  relative  weights  of  an  equal 
number  of  capsules  from  the  finest  plants  in  each  lot : — 

Westerham-crossed     plants     to    self-fertilised 

plants as  100  to  46 

Westerham-crossed  plants  to  intercrossed  plants  as  100  to  54 

Intercrossed  plants  to  self-fertilised  plants        .  as  100  to  86 

We  here  see  how  potent  the  influence  of  a  cross  with  pollen 
from  a  fresh  stock  has  been  on  the  fertility  of  plants  self-fertilised 
for  four  generations,  in  comparison  with  plants  of  the  old  stock 
when  either  intercrossed  or  self-fertilised  for  five  generations ;  the 


CHAP.  VI.  COLOUR   OF   THE   FLOWERS.  203 

flowers  on  all  these  plants  having  been  left  to  be  freely  crossed 
by  insects  or  to  fertilise  themselves.  The  Westerham-crossed 
plants  were  also  much  taller  and  heavier  plants  than  the  self- 
fertilised,  both  in  the  pots  and  open  ground ;  but  they  were  less 
tall  and  heavy  than  the  intercrossed  plants.  This  latter  result, 
however,  would  almost  certainly  have  been  reversed,  if  the 
plants  had  been  allowed  to  grow  for  another  month,  as  the 
Westerham-crossed  were  still  growing  vigorously,  whilst  the 
intercrossed  had  almost  ceased  to  grow.  This  case  reminds  us  of 
the  somewhat  analogous  one  of  Eschscholtzia,  in  which  plants 
raised  from  a  cross  with  a  fresh  stock  did  not  grow  higher  than 
the  self-fertilised  or  intercrossed  plants,  but  produced  a  greater 
number  of  seed-capsules,  which  contained  a  far  larger  average 
number  of  seeds. 

Colour  of  the  Flowers  on  the  above  Three  Lots  of  Plants. — The 
original  mother-plant,  from  which  the  five  successive  self-fertilised 
generations  were  raised,  bore  dingy  purple  flowers.  At  no  time 
was  any  selection  practised,  and  the  plants  were  subjected  in 
each  generation  to  extremely  uniform  conditions.  The  result 
was,  as  in  some  previous  cases,  that  the  flowers  on  all  the  self- 
fertilised  plants,  both  in  the  pots  and  open  ground,  were 
absolutely  uniform  in  tint;  this  being  a  dull,  rather  peculiar 
flesh  colour.  This  uniformity  was  very  striking  in  the  long  row 
of  plants  growing  in  the  open  ground,  and  these  first  attracted 
my  attention.  I  did  not  notice  in  which  generation  the  original 
colour  began  to  change  and  to  become  uniform,  but  I  have  every 
reason  to  believe  that  the  change  was  gradual.  The  flowers  on 
the  intercrossed  plants  were  mostly  of  the  same  tint,  but  not 
nearly  so  uniform  as  those  on  the  self-fertilised  plants,  and  many  of 
them  were  pale,  approaching  almost  to  white.  The  flowers  on  the 
plants  from  the  cross  with  the  purple-flowered  Western  am  stock 
were,  as  might  have  been  expected,  much  more  purple  and  not 
nearly  so  uniform  in  tint.  The  self-fertilised  plants  were  also 
remarkably  uniform  in  height,  as  judged  by  the  eye;  the  inter- 
crossed less  so,  whilst  the  Westerham-crossed  plants  varied  much 
in  height. 

NlCOTIANA   TABACUM. 

This  plant  offers  a  curious  case.  Out  of  six  trials  with  crossed 
and  self-fertilised  plants,  belonging  to  three  successive  genera- 
tions, in  one  alone  did  the  crossed  show  any  marked  superiority 
in  height  over  the  self-fertilised ;  in  four  of  the  trials  they  were 


204  NICOTIANA  TABACUM.  Chap.  V I. 

approximately  equal ;  and  in  one  (i.e.,  in  the  first  generation) 
the  self-fertilised  plants  were  greatly  superior  to  the  crossed. 
In  no  case  did  the  capsules  from  flowers  fertilised  with  pollen 
from  a  distinct  plant  yield  many  more,  and  sometimes  they  yielded 
much  fewer  seeds  than  the  capsules  from  self-fertilised  flowers. 
But  when  the  flowers  of  one  variety  were  crossed  with  pollen 
from  a  slightly  different  variety,  which  had  grown  under 
somewhat  different  conditions,— that  is,  by  a  fresh  stock, — the 
seedlings  derived  from  tins  cross  exceeded  in  height  and  weight 
those  from  the  self-fertilised  flowers  in  an  extraordinary  degree. 

Twelve  flowers  on  some  plants  of  the  common  tobacco,  raised 
from  purchased  seeds,  were  crossed  with  pollen  frqm  a  distinct 
plant  of  the  same  lot,  and  these  produced  ten  capsules.  Twelve 
flowers  on  the  same  plants  were  fertilised  with  their  own  pollen, 
and  produced  eleven  capsules.  The  seeds  in  the  ten  crossed 
capsules  weighed  31  "7  grains,  whilst  those  in  ten  of  the  self- 
fertilised  capsules  weighed  47 '  67  grains ;  or  as  100  to  150.  The 
much  greater  productiveness  of  the  self-fertilised  than  of  the 
crossed  capsules  can  hardly  be  attributed  to  chance,  as  all  the 
capsules  of  both  lots  were  very  fine  and  healthy  ones. 

The  seeds  were  placed  on  sand,  and  several  pairs  in  an  equal 
state  of  germination  were  planted  on  the  opposite  sides  of  three 
pots.  The  remaining  seeds  were  thickly  sown  on  the  two  sides 
of  Pot  IV.,  so  that  the  plants  in  this  pot  were  much  crowded. 
The  tallest  plant  on  each  side  of  each  pot  was  measured.  Whilst 
the  plants  were  quite  young  the  four  tallest  crossed  plants 
averaged  7 -87  inches,  and  the  four  tallest  self-fertilised  14  "87 
inches  in  height ;  or  as  100  to  189.  The  heights  at  this  age  are 
given  in  the  two  left  columns  of  the  following  table. 

When  in  full  flower  the  tallest  plants  on  each  side  were  again 
measured  (see  the  two  right-hand  columns),  with  the  following 
result.  But  I  should  state  that  the  pots  were  not  large  enough, 
and  the  plants  never  grew  to  their  proper  height.  The  four 
tallest  crossed  plants  now  averaged  18  ■  5,  and  the  four  talles+, 
self-fertilised  plants  32  ■  75  inches  in  height ;  or  as  100  to  178 
In  all  four  pots  a  self-fertilised  plant  flowered  before  any  one  ol 
the  crossed. 

In  Pot  IV.,  in  which  the  plants  were  extremely  crowded,  the 
two  lots  were  at  first  equal ;  and  ultimately  the  tallest  crossed 
plant  exceeded  by  a  trifle  the  tallest  self-fertilised  plant.  This 
recalled  to  my  mind  an  analogous  case  in  the  one  generation  of 
Petunia,  in  which  the  self-fertilised  plants  were  throughout 


Chap.  VI.   CROSSED   AND   SELF-FERTILISED   PLANTS.      20/H 


Table  LXXXIV. 

Nicotiana  tabacum  {First  Generation). 


No.  of  Pot. 

May  20,  1868. 

December  6,  1868. 

Crossed 
Plants. 

Self-fertilised 
Plants. 

Crossed 
Plants. 

Self-fertilised 
Plants. 

I. 

Inches. 
15| 

Inches. 

26 

Inches.             Inches. 
40                   44 

II. 

3 

15 

6$       J          43 

III. 

8 

13 1 

16 

33 

IV. 

Crowded. 

5 

5 

114 

11 

Total  in 
inches. 

31-5 

59-5 

74-0 

131-0 

their  growth  taller  than  the  crossed  in  all  the  pots  except 
in  the  crowded  one.  Accordingly  another  trial  was  made,  and 
some  of  the  same  crossed  and  self-fertilised  seeds  of  tobacco 
were  sown  thickly  on  opposite  sides  of  two  additional  pots ;  the 
plants  being  left  to  grow  up  much  crowded.  When  they  were 
between  13  and  14  inches  in  height  there  was  no  difference 
between  the  two  sides,  nor  was  there  any  marked  difference 
when  the  plants  had  grown  as  tall  as  they  could ;  for  in  one  pot 
the  tallest  crossed  plant  was  26s  inches  in  height,  and  exceeded 
by  2  inches  the  tallest  self-fertilised  plant,  whilst  in  the  other 
pot,  the  tallest  crossed  plant  was  shorter  by  3^  inches  than  the 
tallest  self-fertilised  plant,  which  was  22  inches  in  height. 

As  the  plants  did  not  grow  to  their  proper  height  in  the  above 
small  pots  in  Table  LXXXIV.,  four  crossed  and  four  self-fertilised 
plants  were  raised  from  the  same  seed,  and  were  planted  in  pairs 
on  the  opposite  sides  of  four  very  large  pots  containing  rich  soil ; 
so  that  they  were  not  exposed  to  at  all  severe  mutual  competition. 
When  these  plants  were  in  flower  I  neglected  to  measure  them, 
but  record  in  my  notes  that  all  four  self-fertilised  plants  ex- 
ceeded in  height  the  four  crossed  plants  by  2  or  3  inches.  We 
have  seen  that  the  flowers  on  the  original  or  parent-plants  which 
were  crossed  with  pollen  from  a  distinct  plant  yielded  much  fewer 
seeds  than  those  fertilised  with  their  own  pollen ;  and  the  trial 
just  given,  as  well  as  that  in  Table  LXXXIV.,  show  us  clearly 


2ub 


NICOTIANA   TABACUM. 


Chap.  VI. 


that  the  plants  raised  from  the  crossed  seeds  were  inferior  in 
height  to  those  from  the  self-fertilised  seeds ;  but  only  when  not 
greatly  crowded.  When  crowded  and  thus  subjected  to  very  severe 
competition,  the  crossed  and  self-fertilised  plants  were  nearly 
equal  in  height. 

Crossed  and  self-fertilised  Plants  of  the  Second  Generation. — 
Twelve  flowers  on  the  crossed  plants  of  the  last  generation 
growing  in  the  four  large  pots  just  mentioned,  were  crossed  with 
pollen  from  a  crossed  plant  growing  in  one  of  the  other  pots ; 
and  twelve  flowers  on  the  self-fertilised  plants  were  fertilised 
with  their  own  pollen.  All  these  flowers  of  both  lots  pro- 
duced fine  capsules.  Ten  of  the  crossed  capsules  contained  by 
weight  38  "92  grains  of  seeds,  and  ten  of  the  self-fertilised 
capsules  37 "  74  grains ;  or  as  100  to  97.  Some  of  these  seeds  in 
an  equal  state  of  germination  were  planted  in  pairs  on  the 
opposite  sides  of  five  large  pots.  A  good  many  of  the  crossed 
seeds  germinated  before  the  self-fertilised,  and  were  of  course 
rejected.  The  plants  thus  raised  were  measured  when  several 
of  them  were  in  full  flower. 


Table  LXXXV. 

Nicotiana  tabacum  (Second  Generation'). 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 

14| 

78| 

9 

Inches. 

27 1 

8f 

56 

II. 

60 1 
44 1 
10 

16| 

7 

50| 

III. 

57 1 
1| 

87    (A) 

81|(B) 

IV. 

6f 
31 
69| 

19 

43  § 

4 

V. 

99| 

29f 

94 
3 

Total  in  inches. 

511-63 

413-75         l 

Chap.  VI.   CROSSED   AND   SELF-FERTILISED   PLANTS.      207 

The  thirteen  crossed  plants  here  average  39-35,  and  the 
thirteen  self- fertilised  plants  31  •  82  inches  in  height;  or  as  100 
to  81.  But  it  would  be  a  very  much  fairer  plan  to  exclude  all 
the  starved  plants  of  only  10  inches  and  under  in  height ;  and 
in  this  case  the  nine  remaining  crossed  plants  average  53 '84, 
and  the  seven  remaining  self-fertilised  plants  51  ■  78  inches  in 
height,  or  as  100  to  96 ;  and  this  difference  is  so  small  that  the 
crossed  and  self-fertilised  plants  may  be  considered  as  of  equal 
heights. 

In  addition  to  these  plants,  three  crossed  plants  were  planted 
separately  in  three  large  pots,  and  three  self-fertilised  plants  in 
three  other  large  pots,  so  that  they  were  not  exposed  to  any 
competition ;  and  now  the  self-fertilised  plants  exceeded  the 
crossed  in  height  by  a  little,  for  the  three  crossed  averaged  55  ■  91, 
and  the  three  self-fertilised  59 '  16  inches ;  or  as  100  to  106. 

Crossed  and  self-fertilised  Plants  of  the  Third  Generation. — As  I 
wished  to  ascertain,  firstly,  whether  those  self-fertilised  plants  of 
the  last  generation,  which  greatly  exceeded  in  height  their  crossed 
opponents,  would  transmit  the  same  tendency  to  their  offspring, 
and  secondly,  whether  they  possessed  the  same  sexual  constitu- 
tion, I  selected  for  experiment  the  two  self-fertilised  plants 
marked  A  and  B  in  Pot  III.  in  Table  LXXXV.,  as  these  two 


Table  LXXXVL 

Nicotiana  tabacum  (Third  Generation). 

Seedlings  from  the  Self-fertilised  Plant  A  in  Pot  III., 

Table  LXXXV.,  of  the  last  or  Second  Generation. 


No.  of  Pot. 

From  Self-fertilised 

Plant,  crossed  by  a 

Crossed  Plant. 

From  Self- fertilised 
Plant  again  self-ferti- 
lised, forming  the 
Third  Self-fertilised 
Generation. 

I. 

Inches. 

1001 

91 

Inches. 
98 
79 

II. 

110| 

ioo| 

59| 

66| 

III. 

104 

79  f 

IV. 

84  § 

76 1 

110| 
64 1 

557-25 

Total  in  inches. 

666-75 

10 


208 


NICOTIANA   TABACUM. 


Chap.  VI. 


were  of  nearly  equal  height,  and  were  greatly  superior  to  their 
crossed  opponents.  Four  flowers  on  each  plant  were  fertilised 
with  their  own  p  ill  en,  and  four  others  on  the  same  plants  were 
crossed  with  pollen  from  one  of  the  crossed  plants  growing  in 
another  pot.  This  plan  differs  from  that  before  followed,  in 
which  seedlings  from  crossed  plants  again  crossed,  have  been 
compared  with  seedlings  from  self-fertilised  plants  again  self- 
fertilised.  The  seeds  from  the  crossed  and  self-fertilised  capsules 
of  the  above  two  plants  were  placed  in  separate  watch-glasses  and 
compared,  but  were  not  weighed;  and  in  both  cases  those  from 
the  crossed  capsules  seemed  to  be  rather  less  numerous  than 
those  from  the  self-fertilised  capsules.  These  seeds  were  planted 
in  the  usual  manner,  and  the  heights  of  the  crossed  and  self- 
fertilised  seedlings,  when  fully  grown,  are  given  in  the  preceding 
and  following  table,  LXXXVI.  and  LXXXVII. 

The  seven  crossed  plants  in  the  first  of  these  two  tables  average 
95*25,  and  tbe  seven  self-fertilised  79 "6  inches  in  height;  or  as 
100  to  83.  In  half  the  pots  a  crossed  plant,  and  in  the  other 
half  a  self-fertilised  plant  flowered  first. 

We  now  come  to  the  seedlings  raised  from  the  other  parent- 
plant  B. 

Table  LXXXVII. 

Nicotiana  tabacum  {Third  Generation). 

Seedlings  from  the  Self-fertilised  Plant  B  in  Pot  III., 

Table  LXXX  V.,  of  the  last  or  Second  Generation. 


No.  of  Pot 

From  Self-fertilised 

Plant,  crossed  by  a 

Crossed  Plant. 

From  Self-fertilised 
Plant  again  self-ferti- 
lised, forming  the 
Third  Self-fertilised 
Generation.          ] 

I. 

Inches. 
87 1 
49 

Inches. 
72| 
14| 

73 

1103 

106| 
73§ 

II. 

98£ 
0 

III. 

99 
151 

IV. 

97 1 

48 1 

v. 

Total  in  inches. 

48 1 
0 

81| 
61f 

495-50 

641-75 

Chap.  VI.   CKOSSED  AND   3ELF-FEETILISED   PLANTS.      209 

The  seven  crossed  plants  (for  two  of  them  died)  here  average 
70*78  inches,  and  the  nine  self -fertilised  plants  71  "3  inches  in 
height;  or  as  100  to  barely  101.  In  four  out  of  these  five  pots, 
a  self-fertilised  plant  flowered  before  any  one  of  the  crossed 
plants.  So  that,  differently  from  the  last  case,  the  self-fertilised 
plants  are  in  some  respects  slightly  superior  to  the  crossed. 

If  we  now  consider  the  crossed  and  self-fertilised  plants  of  the 
three  generations,  we  find  an  extraordinary  diversity  in  their 
relative  heights.  In  the  first  generation,  the  crossed  plants  were 
inferior  to  the  self-fertilised  as  100  to  178 ;  and  the  flowers  on 
the  original  parent-plants  which  were  crossed  with  pollen  from  a 
distinct  plant  yielded  much  fewer  seeds  than  the  self-fertilised 
flowers,  in  the  proportion  of  100  to  150.  But  it  is  a  strange  fact 
that  the  self-fertilised  plants,  which  were  subjected  to  very  severe 
competition  with  the  crossed,  had  on  two  occasions  no  advan- 
tage over  them.  The  inferiority  of  the  crossed  plants  of  this  first 
generation  cannot  be  attributed  to  the  immaturity  of  the  seeds, 
for  I  carefully  examined  them ;  nor  to  the  seeds  being  diseased 
or  in  any  way  injured  in  some  one  capsule,  for  the  contents  of 
the  ten  crossed  capsules  were  mingled  together  and  a  few  taken 
by  chance  for  sowing.  In  the  second  generation  the  crossed  and 
self-fertilised  plants  were  nearly  equal  in  height.  In  the  third 
generation,  crossed  and  self-fertilised  seeds  were  obtained  from 
two  plants  of  the  previous  generation,  and  the  seedlings  raised 
from  them  differed  remarkably  in  constitution ;  the  crossed  in  the 
one  case  exceeded  the  self- fertilised  in  height  in  the  ratio  of  100 
to  83,  and  in  the  other  case  were  almost  equal.  This  difference 
between  the  two  lots,  raised  at  the  same  time  from  two  plants 
growing  in  the  same  pot,  and  treated  in  every  respect  alike,  as 
well  as  the  extraordinary  superiority  of  the  self-fertilised  over 
the  crossed  plants  in  the  first  generation,  considered  together, 
make  me  believe  that  some  individuals  of  the  present  species 
differ  to  a  certain  extent  from  others  in  their  sexual  affinities  (to 
use  the  term  employed  by  Gartner),  like  closely  allied  species  of 
the  same  genus.  Consequently  if  two  plants  which  thus  differ 
are  crossed,  the  seedlings  suffer  and  are  beaten  by  those  from 
the  self-fertilised  flowers,  in  which  the  sexual  elements  are  of 
the  same  nature.    It  is  known*  that  with  our  domestic  animals 


*  I    have  given    evidence  on      mestication,'  chap,  xviii.  2nd  edit, 
this   head   in   my   '  Variation   of       vol.  ii.  p.  146. 
Animals  and   Plants   under  Do- 


2iQ  NICOTIAN  A   TABACJM.  Chap.  Vl. 

certain  individuals  are  sexually  incompatible,  and  will  not 
produce  offspring,  although  fertile  with  other  individuals.  But 
Kolreuter  has  recorded  a  case  *  which  bears  more  closely  on  our 
present  one,  as  it  shows  that  in  the  genus  Mcotiana  the  varieties 
differ  in  their  sexual  affinities.  He  experimented  on  five 
varieties  of  the  common  tobacco,  and  proved  that  they  were 
varieties  by  showing  that  they  were  perfectly  fertile  when  re- 
ciprocally crossed;  but  one  of  these  varieties,  if  used  either  as 
the  father  or  the  mother,  was  more  fertile  than  any  of  the  others 
when  crossed  with  a  widely  distinct  species,  N.  glutinosa.  As  the 
different  varieties  thus  differ  in  their  sexual  affinities,  there  is 
nothing  surprising  in  the  individuals  of  the  same  variety  differ- 
ing in  a  like  manner  to  a  slight  degree. 

Taking  the  plants  of  the  three  generations  altogether,  the 
crossed  show  no  superiority  over  the  self-fertilised,  and  I  can 
account  for  this  fact  only  by  supposing  that  with  this  species, 
which  is  perfectly  self-fertile  without  insect  aid,  most  of  the  indi- 
viduals are  in  the  same  condition,  as  those  of  the  same  variety 
of  the  common  pea  and  of  a  few  other  exotic  plants,  which 
have  been  self-fertilised  for  many  generations.  In  such  cases  a 
cross  between  two  individuals  does  no  good;  nor  does  it  in  any 
case,  unless  the  individuals  differ  in  general  constitution,  either 
from  so-called  spontaneous  variation,  or  from  their  progenitors 
having  been  subjected  to  different  conditions.  I  believe  that 
this  is  the  true  explanation  in  the  present  instance,  because,  as 
we  shall  immediately  see,  the  offspring  of  plants,  which  did  not 
profit  at  all  by  being  crossed  with  a  plant  of  the  same  ttock, 
profited  to  an  extraordinary  degree  by  a  cross  with  a  slightly 
different  sub-variety. 

The  Effects  of  a  Gross  with  afresh  Stock. — I  procured  some  seed 
of  N.  tabacum  from  Kew  and  raised  some  plants,  which  formed 
a  slightly  different  sub-variety  from  my  former  plants ;  as  the 
flowers  were  a  shade  pinker,  the  leaves  a  little  more  pointed,  and 
the  plants  not  quite  so  tall.  Therefore  the  advantage  in  height 
which  the  seedlings  gained  by  this  cross  cannot  be  attributed  to 
direct  inheritance.  Two  of  the  plants  of  the  third  self-fertilised 
generation,  growing  in  Pots  II.  and  V.  in  Table  LXXXVIL, 
which  exceeded  in  height  their  crossed  opponents  (as  did  their 
parents  in  a  still  higher  degree)  were  fertilised  with  pollen 
from  the  Kew  plants,  tbat  is,  by  a  fresh  stock.     The  seedlings 


'  Das  Geschlocht  der  Pflanzen,  Zweite  Fortsetzung,'  1764,  p.  55-60. 


Chap.  VI.  GROSS   WITH   A   FRESH   STOCK.  211 

thus  raised  may  be  called  the  Kew-crossed.  Some  other  flowers 
on  the  same  two  plants  were  fertilised  with  their  own  pollen, 
and  the  seedlings  thus  raised  form  the  fourth  self-fertilised 
generation.  The  crossed  capsules  produced  by  the  plant  in 
Pot  II.,  Table  LXXXVII.,  were  plainly  less  fine  than  the  self- 
fertilised  capsules  on  the  same  plant.  In  Pot  V.  the  one  finest 
capsule  was  also  a  self-fertilised  one;  but  the  seeds  produced 
by  the  two  crossed  capsules  together  exceeded  in  number  those 
produced  by  the  two  self-fertilised  capsules  on  the  same  plant. 
Therefore  as  far  as  the  flowers  on  the  parent-plants  are  con- 
cerned, a  cross  with  pollen  from  a  fresh  stock  did  little  or  no 
good ;  and  I  did  not  expect  that  the  offspring  would  have  re- 
ceived any  benefit,  but  in  this  I  was  completely  mistaken. 

The  crossed  and  self-fertilised  seeds  from  the  two  plants  were 
placed  on  bare  sand,  and  very  many  of  the  crossed  seeds  of  both 
sets  germinated  before  the  self-fertilised  seeds,  and  protruded 
their  radicles  at  a  quicker  rate.  Hence  many  of  the  crossed 
seeds  had  to  be  rejected,  before  pairs  in  an  equal  state  of  germina- 
tion were  obtained  for  planting  on  the  opposite  sides  of  sixteen 
large  pots.  The  two  series  of  seedlings  raised  from  the  parent- 
plants  in  the  two  Pots  II.  and  V.  were  kept  separate,  and  when 
fully  grown  were  measured  to  the  tips  of  their  highest  leaves,  as 
shown  in  the  following  double  table.  But  as  there  was  no  uniform 
difference  in  height  between  the  crossed  and  self-fertilised  seed- 
lings raised  from  the  two  plants,  their  heights  have  been  added 
together  in  calculating  the  averages.  I  should  state  that  by  the 
accidental  fall  of  a  large  bush  in  the  greenhouse,  several  plants 
in  both  the  series  were  much  injured.  These  were  at  once 
measured  together  with  their  opponents  and  afterwards  thrown 
away.  The  others  were  left  to  grow  to  their  full  height,  and 
were  measured  when  in  flower.  This  accident  accounts  for  the 
small  height  of  some  of  the  pairs ;  but  as  all  the  pairs,  whether 
only  partly  or  fully  grown,  were  measured  at  the  same  time,  the 
measurements  are  fair. 

The  average  height  of  the  twenty-six  crossed  plants  in  the  six- 
teen pots  of  the  two  series  is  63*29,  and  that  of  the  twenty- 
six  self-fertilised  plants  is  41  ■  67  inches  ;  or  as  100  to  66.  The 
superiority  of  the  crossed  plants  was  shown  in  another  way, 
for  in  every  one  of  the  sixteen  pots  a  crossed  plant  flowered 
before  a  self-fertilised  one,  with  the  exception  of  Pot  VI.  of  the 
second  series,  in  which  the  plants  on  the  two  sides  flowered 
simultaneously. 


212 


NICOTIANA    TABACUM. 


Chap.  VI. 


Table  LXXXVIII. 

Nicotiana  tabacum. 

Plants  raised  from  two  Plants  of  the  Third  Self-fertilised 
Generation  in  Pots  II.  and  V.,  in  Table  LXXX  VJI. 


From  Pot  II.,  Table  LXXXVIL 


Total 


No.  of  Pot 

Plants  of  the 
Kew-crossed  1    Fourth  Self- 
Plants,       fertilised  Gen- 
eration. 

I. 

Inches. 
84§ 
31 

Inches. 

68 1 

5 

II. 

78£ 
48 

511 

70 

III. 

77 1 
77^ 

12| 

.         6§ 

IV. 

49 1 
15g 

29 1 
32 

V. 

89 
17 

85 

VI. 

90         1         80 

VII. 

84 1 
76 1 

48 1 
56 1 

VIII. 

83 1 

84 1 

From  Pot  V.,  Table  LXXXVIL 


No.  of  Pot. 


II. 


III. 


IV. 


VI. 


VII. 


VIII. 


,ta\  in)        902-63  '       636-13        To.tal,  inj 
inches. J  mcnes.J 


Kew-crossed 
Plants. 


Inches. 
77 1 

71 


55 1 
18 


76| 


90j 

22| 


94  j 


78 


85| 


65 1 

72* 


743-13 


Plants  of  the 
Fourth  Self- 
fertilised  Gen- 
eration. 


Inches. 
56 
5? 


27! 
7 


60| 


1 1  6 

4-1 


28  { 


78| 


61, 


78| 

274 


-447-38 


Some  of  the  remaining  seeds  of  both  series,  whether  or  not  in 
a  state  of  germination,  were  thickly  sown  on  the  opposite  sides 
of  two  very  large  pots ;  and  the  six  highest  plants  on  each  side 
of  each  pot  were  measured  after  they  had  grown  to  nearly  their 
full  height.  But  their  heights  were  mnch  less  than  in  the 
former  trials,  owing  to  their  extremely  crowded  condition.  Even 
whilst  quite  young,  the  crossed  seedlings  manifestly  had  much 
broader  and  finer  leaves  than  the  self-fertilised  seedlings. 


(JHM\  VI. 


CROSS  WITH  A  FRESH  STOCK. 


218 


Table  LXXXIX. 

Nicotian  a  tabacum. 

Plants  of  the  same  parentage  as  those  in  Table  L XXXVIII., 
but  grown  extremely  crowded  in  two  large  pots. 


From  Pot  II.,  Table  LXXX  VTT. 

From  Pot  V.,  Table  LX  XXVII. 

Kew-crossed 
Plants. 

Plants  of  the 
Fourth  Self-ferti- 
lised Generation. 

Kew-crossed 
Plants. 

Plants  of  the 
Fourth  Self-ferti- 
lised Generation 

Inches. 
42 1 
34 
30 1 
23 1 
26f 
18| 

Inches. 
22| 
19| 
14f 
16 
13| 
16 

Inches. 
44 1 
42  j 
27 1 
31§ 
32 
24§ 

Inches. 
22| 
21 
18 
15| 
13| 
14| 

175-63 

101-50 

202-75 

105-13 

The  twelve  tallest  crossed  plants  in  the  two  pots  belonging  to 
the  two  series  average  here  31 '  53,  and  the  twelve  tallest  self-ferti- 
lised plants  17 "21  inches  in  height;  or  as  100  to  54.  The  plants 
on  both  sides,  when  fully  grown,  some  time  after  they  had  been 
measured,  were  cut  down  close  to  the  ground  and  weighed. 
The  twelve  crossed  plants  weighed  21*25  ounces;  and  the 
twelve  self-fertilised  plants  only  7 "  83  ounces ;  or  in  weight  as 
100  to  37. 

The  rest  of  the  crossed  and  self-fertilised  seeds  from  the  two 
parent-plants  (the  same  as  in  the  last  experiment)  was  sown  on 
the  1st  of  July  in  four  long  parallel  and  separate  rows  in  good  soil 
in  the  open  ground ;  so  that  the  seedlings  were  not  subjected  to 
any  mutual  competition.  The  summer  was  wet  and  unfavourable 
for  their  growth.  Whilst  the  seedlings  were  very  small  the  two 
crossed  rows  had  a  clear  advantage  over  the  two  self-fertilised 
rows.  When  fully  grown  the  twenty  tallest  crossed  plants  and 
the  twenty  tallest  self-fertilised  plants  were  selected  and  mea- 
sured on  the  11th  of  November  to  the  extremities  of  their  leaves, 
as  shown  in  the  following  table  (XC).  Of  the  twenty  crossed 
plants,  twelve  had  flowered ;  whilst  of  the  twenty  self-fertilised 
plants  one  alone  had  flowered. 


214 


NICOTIAN  \   TABACUM. 


Chap.  VI. 


Table  XC. 

Nicotiana  tabacum. 

Plants  raised  from  the  same  seeds  as  in  the  last  two  experiments, 

hut  sown  separately  in  the  open  ground,  so  as  not  to  compete 

together. 


From  Pot  II.,  Table  LXXXVII. 

From  Pot  V.,  Table  LXXXVII. 

Kew-crossed 
Plants. 

Plants  of  the 
Fourth  Self-ferti- 
lised Generation. 

Kew-crossed 
Plants. 

Plants  of  the 
Fourth  Self-ferti- 
lised Generation. 

Inches. 

42  f 
54 1 
39f 
53| 
49  f 

50|        ' 
47  J 
57 1 
37 
48 

1 
Inches. 

37 1 
34  4 

30 

28| 

Dig 

25| 

26  § 
22 1 
28 

Inches. 
54 1 
51 | 
45 
43 
43 
48! 
44 
48§ 
55  • 
63 

Inches. 
34  J 
38f 
40! 
43 1 
40 
38 1 

OK  6 

39! 
47| 
58 1 

478-75 

286-86       ! 

i 

496-13 

417-25 

The  twenty  tallest  crossed  plants  here  average  48 -74,  and  the 
twenty  tallest  self-fertilised  35  ■  2  inches  in  height ;  or  as  100  to 
72.  These  plants  after  being  measured  were  cut  down  close  to 
the  ground,  and  the  twenty  crossed  plants  weighed  195*75 
ounces,  and  the  twenty  self-fertilised  plants  123  ■  25  ounces ;  or 
as  100  to  63. 

In  the  three  preceding  tables,  LXXXVIIL,  LXXXIX.,  and 
XC,  we  have  the  measurements  of  fifty-six  plants  derived  from 
two  plants  of  the  third  self-fertilised  generation  crossed  with 
pollen  from  a  fresh  stock,  and  of  fifty-six  plants  of  the  fourth  self- 
fertilised  generation  derived  from  the  same  two  plants.  These 
crossed  and  self-fertilised  plants  were  treated  in  three  different 
ways,  having  been  put,  firstly,  into  moderately  close  competition 
with  one  another  in  pots ;  secondly,  having  been  subjected  to 
unfavourable  conditions  and  to  very  severe  competition  from 
being  greatly  crowded  in  two  large  pots ;  and  thirdly,  having 
being  sown  separately  in  open  and  good  ground,  so  as  not  to 
suffer  from  any  mutual  competition.  In  all  these  cases  the 
crossed  plants  in  each  lot  were  greatly  superior  to  the  self- 


Chap.  VI.  CYCLAMEN   PERSICUM.  215 

fertilised.  This  was  shown  in  several  ways, — by  the  earlier 
germination  of  the  crossed  seeds,  by  the  more  rapid  growth  of 
the  seedlings  whilst  quite  young,  by  the  earlier  flowering  of  the 
mature  plants,  as  well  as  by  the  greater  height  which  they 
ultimately  attained.  The  superiority  of  the  crossed  plants  was 
shown  still  more  plainly  when  the  two  lots  were  weighed  ;  the 
weight  of  the  crossed  plants  to  that  of  the  self-fertilised  in  the 
two  crowded  pots  being  as  100  to  37.  Better  evidence  could 
hardly  be  desired  of  the  immense  advantage  derived  from  a 
cross  with  afresh  stock. 

XXVI.  PEIMULACE^l.— Cyclamen  persicttm.* 

Ten  flowers  crossed  with  pollen  from  plants  known  to  be 
distinct  seedlings,  yielded  nine  capsules,  containing  on  an 
average  34*2  seeds,  with  a  maximum  of  seventy-seven  in  one. 
Ten  flowers  self-fertilised  yielded  eight  capsules,  containing  on 
an  average  only  13  ■  1  seeds,  with  a  maximum  of  twenty-five  in  one. 
This  gives  a  ratio  of  100  to  38  for  the  average  number  of  seeds 
per  capsule  for  the  crossed  and  self-fertilised  flowers.  The 
flowers  hang  downwards,  and  as  the  stigmas  stand  close  beneath 
the  anthers,  it  might  have  been  expected  that  pollen  would 
have  fallen  on  them,  and  that  they  would  have  been  spontaneously 
self- fertilised ;  but  these  covered-up  plants  did  not  produce  a 
single  capsule.  On  some  other  occasions  uncovered  plants  in 
the  same  greenhouse  produced  plenty  of  capsules,  and  I  suppose 
that  the  flowers  had  been  visited  by  bees,  which  could  hardly 
fail  to  carry  pollen  from  plant  to  plant. 

The  seeds  obtained  in  the  manner  just  described  were  placed 
on  sand,  and  after  germinating  were  planted  in  pairs, — three 
crossed  and  three  self-fertilised  plants  on  the  opposite  sides  of 
four  pots.  When  the  leaves  were  2  or  3  inches  in  length, 
including  the  foot-stalks,  the  seedlings  on  both  sides  were 
equal.  In  the  course  of  a  month  or  two  the  crossed  plants  began 
to  show  a  slight  superiority  over  the  self-fertilised,  which 
steadily  increased ;  and  the  crossed  flowered  in  all  four  pots  some 
weeks  before,  and  much  more  profusely  than  the  self-fertilised. 
The  two  tallest  flower-stems  on  the  crossed  plants  in  each  pot 
were  now  measured,  and  the  average  height  of  the  eight  stems 


*  Cyclamen  repandum,  accord-  p.  150),  is  proterandrous,  and  this 
ing  to  Lecoq  ('  Geographie  Botan-  I  believe  to  be  the  case  with  C. 
ique  de.  1'Europe,'  torn.  viii.  1858,       persicum. 


216 


CYCLAMEN   PEESICUM. 


Chap.  VI. 


was  9  "49  inches.  After  a  considerable  interval  of  time  the 
self-fertilised  plants  flowered,  and  several  of  their  flower-stems 
(but  I  forgot  to  record  how  many)  were  ronghly  measured,  and 
their  average  height  was  a  little  under  7 "  5  inches ;  so  that  the 
flower-stems  on  the  crossed  plants  to  those  on  the  self-fertilised 
were  at  least  as  100  to  79.  The  reason  why  I  did  not  make 
more  careful  measurements  of  the  self-fertilised  plants  was,  that 
they  looked  such  poor  specimens  that  I  determined  to  have  them 
re-potted  in  larger  pots  and  in  the  following  year  to  measure 
them  carefully ;  but  we  shall  see  that  this  was  partly  frustrated 
by  so  few  flower-stems  being  then  produced. 

These  plants  were  left  uncovered  in  the  greenhouse ;  and  the 
twelve  crossed  plants  produced  forty  capsules,  whilst  the 
twelve  self-fertilised  plants  produced  only  five ;  or  as  100  to  12. 
But  this  difference  does  not  give  a  just  idea  of  the  relative 
fertility  of  the  two  lots.  I  counted  the  seeds  in  one  of  the  finest 
capsules  on  the  crossed  plants,  and  it  contained  seventy-three ; 
whilst  the  finest  of  the  five  capsules  produced  by  the  self- 
fertilised  plants  contained  only  thirty-five  good  seeds.  In  the 
other  four  capsules  most  of  the  seeds  were  barely  half  as  large 
as  those  in  the  crossed  capsules. 

Table  XOI. 
Cyclamen  persicum :  0  implies  that  no  flower-stem  was  produced. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

Inches. 

Inches. 

I. 

10 

0 

n 

0 

10§ 

0 

II. 

91 

0 

10 

0 

10| 

0 

III. 

H 

8 

9g 

H 

9| 

6| 

IV. 

Hi 

0 

10f 

n 

10§ 

0 

Total  in  inches. 

119-88 

29-50 

Chap.  VI.  ANAGALLIS  COLLINA.  217 

In  the  following  year  the  crossed  plants  again  bore  many 
flowers  before  the  self-fertilised  bore  a  single  one.  The  three 
tallest  flower-stems  on  the  crossed  plants  in  each  of  the  pots 
were  measured,  as  shown  in  Table  XCI.  In  Pots  I.  and  II.  the 
self-fertilised  plants  did  not  produce  a  single  flower-stem;  in 
Pot  IV.  only  one ;  and  in  Pot  III.  six,  of  which  the  three  tallest 
were  measured. 

The  average  height  of  the  twelve  flower-stems  on  the  crossed 
plants  is  9*99,  and  that  of  the  four  flower-stems  on  the  self- 
fertilised  plants  7  •  37  inches  ;  or  as  100  to  74.  The  self-fertilised 
plants  were  miserable  specimens,  whilst  the  crossed  ones  looked 
very  vigorous. 

Anagallis. 

Anagallis  collina,  var.  grandiflora  (pale  red  and  blue-flowered 
sub-varieties). 

Firstly,  twenty-five  flowers  on  some  plants  of  the  red  variety 
were  crossed  with  pollen  from  a  distinct  plant  of  the  same 
variety,  and  produced  ten  capsules ;  thirty-one  flowers  were 
fertilised  with  their  own  pollen,  and  produced  eighteen  capsules. 
These  plants,  which  were  grown  in  pots  in  the  greenhouse,  were 
evidently  in  a  very  sterile  condition,  and  the  seeds  in  both 
sets  of  capsules,  especially  in  the  self-fertilised,  although 
numerous,  were  of  so  poor  a  quality  that  it  was  very  difficult 
to  determine  which  were  good  and  which  bad.  But  as  far  as  I 
could  judge,  the  crossed  capsules  contained  on  an  average  6*3 
good  seeds,  with  a  maximum  in  one  of  thirteen ;  whilst  the 
self- fertilised  contained  6  ■  05  such  seeds,  with  a  maximum  in 
one  of  fourteen. 

Secondly,  eleven  flowers  on  the  red  variety  were  castrated 
whilst  young  and  fertilised  with  pollen  from  the  blue  variety, 
and  this  cross  evidently  much  increased  their  fertility;  for  the 
eleven  flowers  yielded  seven  capsules,  which  contained  on  an 
average  twice  as  many  good  seeds  as  before,  viz.,  12  ■  7  ;  with  a 
maximum  in  two  of  the  capsules  of  seventeen  seeds.  Therefore 
these  crossed  capsules  yielded  seeds  compared  with  those  in  the 
foregoing  self-fertilised  capsules,  as  100  to  48.  These  seeds  were 
also  conspicuously  larger  than  those  from  the  cross  between  two 
individuals  of  the  same  red  variety,  and  germinated  much  more 
freely.  The  flowers  on  most  of  the  plants  produced  by  the  cross 
between  the  two-coloured  varieties  (of  which  several  were  raised), 


218 


ANAGALLIS   COLLINA. 


Chap.  VI. 


took  after  their  mother,  and  were  red-coloured.  But  on  two  of 
the  plants  the  flowers  were  plainly  stained  with  blue,  and  to 
such  a  degree  in  one  case  as  to  be  almost  intermediate  in  tint. 

The  crossed  seeds  of  the  two  foregoing  kinds  and  the  self- 
fertilised  were  sown  on  the  opposite  sides  of  two  large  pots,  and 
the  seedlings  were  measured  when  fully  grown,  as  shown  in  the 
two  following  tables  : — 

Table  XCIL 

Anagallis  collina. 


Red  Variety  crossed  by  a  distinct  Plant  of  tbe  Red  Variety, 
and  Red  Variety  Self-fertilised. 

No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
23 1 
21 
171 

Inches. 
15| 
15f 
14 

Total  in  inches. 

61-75 

45-00 

Red  Variety  crossed  by  Blue  Variety,  and  Red  Variety 
Self-fertilised. 

No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

II. 

Inches. 
30| 

27 1 
25 

Inches. 
24< 
18! 
HI 

Total  in  inches. 

82-88 

54-75 

Total  of  both  lots. 

144-63 

99-75 

As  the  plants  of  the  two  lots  are  few  in  number,  they  may  be 
run  together  for  the  general  average ;  but  I  may  first  state  that 
the  height  of  the  seedlings  from  the  cross  between  two  individuals 
of  the  red  variety  is  to  that  of  the  self-fertilised  plants  of  the  red 
variety  as  100  to  73  ;  whereas  the  height  of  the  crossed  offspring 
from  the  two  varieties  to  the  self-fertilised  plants  of  the  red 
variety  is  as  100  to  66.  So  that  the  cross  between  the  two 
varieties  is  here  seen  to  be  the  most  advantageous.  The  average 
height  of  all  six  crossed  plants  in  the  two  lots  taken  together  is 


Chap.  VI.  PRIMULA   VEEIS.  219 

48 '20,  and  that  of  the  six  self-fertilised  plants  33 '25 ;  or  as  100 
to  69. 

These  six  crossed  plants  produced  spontaneously  twenty-six 
capsules,  whilst  the  six  self-fertilised  plants  produced  only  two, 
or  as  100  to  8.  There  is  therefore  the  same  extraordinary 
difference  in  fertility  between  the  crossed  and  self-fertilised 
plants  as  in  the  last  genus,  Cyclamen,  which  belongs  to  the  same 
family  of  the  Primulaceae. 

Primula  veris.    Brit.  Flora. 

(  Var.  officinalis,  Linn.}.     The  Cowslip. 

Most  of  the  species  in  this  genus  are  heterostyled  or 
dimorphic  ;  that  is,  they  present  two  forms,— one  long-styled  with 
short  stamens,  and  the  other  short-styled  with  long  stamens.* 
For  complete  fertilisation  it  is  necessary  that  pollen  from  the  one 
form  should  be  applied  to  the  stigma  of  the  other  form ;  and  this 
is  effected  under  nature  by  insects.  Such  unions,  and  the  seed- 
lings raised  from  them,  I  have  called  legitimate.  If  one  form  is 
fertilised  with  pollen  from  the  same  form,  the  full  complement 
of  seed  is  not  produced ;  and  in  the  case  of  some  heterostyled 
genera  no  seed  at  all  is  produced.  Such  unions,  and  the  seed- 
lings raised  from  them,  I  have  called  illegitimate.  These  seed- 
lings are  often  dwarfed  and  more  or  less  sterile,  like  hybrids. 
I  possessed  some  long-styled  plants  of  P.  veris,  which  during  four 
successive  generations  had  been  produced  from  illegitimate 
unions  between  long-styled  plants ;  they  were,  moreover,  in  some 
degree  inter-related,  and  had  been  subjected  all  the  time  to  similar 
conditions  in  pots  in  the  greenhouse.  As  long  as  they  were 
cultivated  in  this  manner,  they  grew  well  and  were  healthy  and 
fertile.  Their  fertility  even  increased  in  the  later  generations, 
as  if  they  were  becoming  habituated  to  illegitimate  fertilisation. 
Plants  of  the  first  illegitimate  generation  when  taken  from  the 
greenhouse  and  planted  in  moderately  good  soil  out  of  doors 
grew  well  and  were  healthy;  but  when  those  of  the  two  last 
illegitimate  generations  were  thus  treated  they  became  exces- 


*  See  my  paper  '  On  the  Two  like  Nature  of  the  Offspring  from 

Forms  or  Dimorphic  Condition  in  the  Illegitimate  Unions  of  Dimor- 

the  Species  of  Primula,'  in  '  Jour-  phic  and  Trimorphic  Plants,'  wa8 

nalofProc.  Linn.  Sua' vol.  vi.  1862,  published  in  vol.  x.  1867,  p.  393, 

p.  77.     A  second  paper,  to  which  of  the  same  journal. 
I  presently  refer,  '  On  the  Hybrid- 


220  PRIMULA   VERIS.  Chap.  VI. 

sively  sterile  and  dwarfed,  and  remained  so  during  the  following 
year,  by  which  time  they  ought  to  have  become  accustomed  to 
growing  out  of  doors,  so  that  they  must  have  possessed  a  weak 
constitution. 

Under  these  circumstances,  it  seemed  advisable  to  ascertain 
what  would  be  the  effect  of  legitimately  crossing  long-styled 
plants  of  the  fourth  illegitimate  generation  with  pollen  taken  from 
non-related  short-styled  plants,  growing  under  different  con- 
ditions. Accordingly  several  flowers  on  plants  of  the  fourth 
illegitimate  generation  (i.e.,  great-great-grandchildren  of  plants 
which  had  been  legitimately  fertilised),  growing  vigorously  in  pots 
in  the  greenhouse,  were  legitimately  fertilised  with  pollen  from 
an  almost  wild  short-styled  cowslip,  and  these  flowers  yielded 
some  fine  capsules.  Thirty  other  flowers  on  the  same  illegi- 
timate plants  were  fertilised  with  their  own  pollen,  and  these 
yielded  seventeen  capsules,  containing  on  an  average  thirty-two 
seeds.  This  is  a  high  degree  of  fertility ;  higher,  I  believe,  than 
that  which  generally  obtains  with  illegitimately  fertilised  long- 
styled  plants  growing  out  of  doors,  and  higher  than  that  of  the 
previous  illegitimate  generations,  although  their  flowers  were 
fertilised  with  pollen  taken  from  a  distinct  plant  of  the  same 
form. 

These  two  lots  of  seeds  were  sown  (for  they  will  not  germinate 
well  when  placed  on  bare  sand)  on  the  opposite  sides  of  four 
pots,  and  the  seedlings  were  thinned,  so  that  an  equal  number 
were  left  on  the  two  sides.  For  some  time  there  was  no  marked 
difference  in  height  between  the  two  lots  ;  and  in  Pot  III.,  Table 
XCIIL,  the  self-fertilised  plants  were  rather  the  tallest.  But  by 
the  time  that  they  had  thrown  up  young  flower-stems,  the 
legitimately  crossed  plants  appeared  much  the  finest,  and  had 
greener  and  larger  leaves.  The  breadth  of  the  largest  leaf  on 
each  plant  was  measured,  and  those  on  the  crossed  plants  were 
on  an  average  a  quarter  of  an  inch  (exactly  "28  of  an  inch) 
broader  than  those  on  the  self-fertilised  plants.  The  plants,  from 
being  too  much  crowded,  produced  poor  and  short  flower-stems. 
The  two  finest  on  each  side  were  measured ;  the  eight  on  the 
legitimately  crossed  plants  averaged  4 '08,  and  the  eight  on  the 
illegitimately  self-fertilised  plants  averaged  2*93  inches  in 
height;  or  as  100  to  72. 

These  plants  after  they  had  flowered  were  turned  out  of  their 
pots,  and  planted  in  fairly  good  soil  in  the  open  ground.  In 
the  following  year  (1870),  when  in  full  flower,  the  two  tallest 


Chap.  VI. 


PRIMULA   VERIS. 


221 


flower  stems  on  each  side  were  again  measured,  as  shown  in  the 
following  table,  which  likewise  gives  the  number  of  flower-stems 
produced  on  both  sides  of  all  the  pots. 


Table  XCIII, 

Primula  veris. 


No.  of  Pot. 

Legitimately  crossed  Plants. 

Illegitimatelv  self-fertilised 
Plants. 

Height  in 
inches. 

No.  of  Flower- 
stems  pro- 
duced. 

Height  in     No+ of  Flower- 
inches,          "pro- 
duced. 

I. 

9 
8 

16 

9  i 

3 

II. 

7         J          16 
6! 

6 
tS4 

3 

III. 

6 

6| 

16 

3 

0g 

4 

IV. 

71 

68 

14 

2| 

94 

Z3 

5 

Total. 

56-26 

62 

25-75 

15        ] 

The  average  height  of  the  eight  tallest  flower-stems  on  the 
crossed  plants  is  here  7 "  03  inches,  and  that  of  the  eight  tallest 
flower-stems  on  the  self-fertilised  plants  3 '  21  inches ;  or  as  100 
to  46.  We  see,  also,  that  the  crossed  plants  bore  sixty-two  flower- 
stems;  that  is,  above  four  times  as  many  as  those  (viz.,  fifteen) 
borne  by  the  self-fertilised  plants.  The  flowers  were  left  ex- 
posed to  the  visits  of  insects,  and  as  many  plants  of  both  forms 
grew  close  by,  they  must  have  been  legitimately  and  naturally  fer- 
tilised. Under  these  circumstances  the  crossed  plants  produced 
324  capsules,  whilst  the  self-fertilised  produced  only  16 ;  and 
these  were  all  produced  by  a  single  plant  in  Pot  II.,  which  was 
much  finer  than  any  other  self-fertilised  plant.  Judging  by  the 
number  of  capsules  produced,  the  fertility  of  an  equal  number 
of  crossed  and  self-fertilised  plants  was  as  100  to  5. 

In  the  succeeding  year  (1871)  I  did  not  count  all  the  flower- 
stems  on  these  plants,  but  only  those  which  produced  cap- 
sules containing  good  seeds.  The  season  was  unfavourable,  and 
the  crossed  plants  produced  only  forty  such  flower-stems,  bearing 


222  PRIMULA   VERIS.  Chap.  VI. 

168  good  capsules,  whilst  the  self-fertilised  plants  produced 
only  two  such  flower-stems,  bearing  only  6  capsules,  half  of 
which  were  very  poor  ones.  So  that  the  fertility  of  the  two  lots, 
judging  by  the  number  of  capsules,  was  as  100  to  3 '  5. 

In  considering  the  great  difference  in  height  and  the  wonderful 
difference  in  fertility  between  the  two  sets  of  plants,  we  should 
bear  in  mind  that  this  is  the  result  of  two  distinct  agencies. 
The  self-fertilised  plants  were  the  product  of  illegitimate  fertili- 
sation during  five  successive  generations,  in  all  of  which,  ex- 
cepting the  last,  the  plants  had  been  fertilised  with  pollen  taken 
from  a  distinct  individual  belonging  to  the  same  form,  but  which 
was  more  or  less  closely  related.  The  plants  had  also  been 
subjected  in  each  generation  to  closely  similar  conditions.  This 
treatment  alone,  as  I  know  from  other  observations,  would  have 
greatly  reduced  the  size  and  fertility  of  the  offspring.  On  the 
other  hand,  the  crossed  plants  were  the  offspring  of  long-styled 
plants  of  the  fourth  illegitimate  generation  legitimately  crossed 
with  pollen  from  a  short-styled  plant,  which,  as  well  as  its  pro- 
genitors, had  been  exposed  to  very  different  conditions ;  and  this 
latter  circumstance  alone  would  have  given  great  vigour  to  the 
offspring,  as  we  may  infer  from  the  several  analogous  cases 
already  given.  How  much  proportional  weight  ought  to  be  at- 
tributed to  these  two  agencies, — the  one  tending  to  injure  the 
self-fertilised  offspring,  and  the  other  to  benefit  the  crossed 
offspring, — cannot  be  determined.  But  we  shall  immediately 
see  that  the  greater  part  of  the  benefit,  as  far  as  increased 
fertility  is  concerned,  must  be  attributed  to  the  cross  having 
been  made  with  a  fresh  stock. 

Primula  veris. 

Equal-styled  and  red-flowered  var. 

I  have  described  in  my  paper  '  On  the  Illegitimate  Unions  of 
Dimorphic  and  Trimorphic  Plants '  this  remarkable  variety,  which 
was  sent  to  me  from  Edinburgh  by  Mr.  J.  Scott.  It  possessed  a 
pistil  proper  to  the  long-styled  form,  and  stamens  proper  to  the 
short-styled  form  ;  so  that  it  had  lost  the  heterostyled  or  dimor- 
phic character  common  to  most  of  the  species  of  the  genus, 
and  may  be  compared  with  an  hermaphrodite  form  of  a  bi- 
sexual animal.  Consequently  the  pollen  and  stigma  of  the 
same  flower  are  adapted  for  complete  mutual  fertilisation,  instead 
of  its  being  necessary  that  pollen  should  be  brought  from  one 


Chap.  VI.  EQUAL-STYLED   VARIETY.  223 

form  to  another,  as  in  the  common  cowslip.  From  the  stigma 
and  anthers  standing  nearly  on  the  same  level,  the  flowers  are 
perfectly  self-fertile  when  insects  are  excluded.  Owing  to  the 
fortunate  existence  of  this  variety,  it  is  possible  to  fertilise  its 
flowers  in  a  legitimate  manner  with  their  own  pollen,  and  to 
cross  other  flowers  in  a  legitimate  manner  with  pollen  from 
another  variety  or  fresh  stock.  Thus  the  offspring  from  both 
unions  can  be  compared  quite  fairly,  free  from  any  doubt  from 
the  injurious  effects  of  an  illegitimate  union. 

The  plants  on  which  I  experimented  had  been  raised  during 
two  successive  generations  from  spontaneously  self-fertilised 
seeds  produced  by  plants  under  a  net ;  and  as  the  variety  is 
highly  self- fertile,  its  progenitors  in  Edinburgh  may  have  been 
self-fertilised  during  some  previous  generations.  Several  flowers 
on  two  of  my  plants  were  legitimately  crossed  with  pollen  from 
a  short-styled  common  cowslip  growing  almost  wild  in  my 
orchard ;  so  that  the  cross  was  between  plants  which  had  been 
subjected  to  considerably  different  conditions.  Several  other 
flowers  on  the  same  two  plants  were  allowed  to  fertilise  them- 
selves under  a  net ;  and  this  union,  as  already  explained,  is  a 
legitimate  one. 

The  crossed  and  self-fertilised  seeds  thus  obtained  were  sown 
thickly  on  the  opposite  sides  of  three  pots,  and  the  seedlings 
thinned,  so  that  an  equal  number  were  left  on  the  two  sides. 
The  seedlings  during  the  first  year  were  nearly  equal  in 
height,  excepting  in  Pot  III.,  Table  XCIV.,  in  which  the  self- 
fertilised  plants  had  a  decided  advantage.  In  the  autumn  the 
plants  were  bedded  out,  in  their  pots;  owing  to  this  circum- 
stance, and  to  many  plants  growing  in  each  pot,  they  did  not 
flourish,  and  none  were  very  productive  in  seeds.  But  the 
conditions  were  perfectly  equal  and  fair  for  both  sides.  In  the 
following  spring  I  record  in  my  notes  that  in  two  of  the  pots 
the  crossed  plants  are  "  incomparably  the  finest  in  general 
appearance,"  and  in  all  three  pots  they  flowered  before  the  self- 
fertilised.  When  in  full  flower  the  tallest  flower-stem  on  each 
side  of  each  pot  was  measured,  and  the  number  of  the  flower- 
stems  on  both  sides  counted,  as  shown  in  the  following  table. 
The  plants  were  left  uncovered,  and  as  other  plants  were  growing 
close  by,  the  flowers  no  doubt  were  crossed  by  insects.  When 
the  capsules  were  ripe  they  were  gathered  and  counted,  and 
the  result  is  likewise  shown  in  the  following  table ;— 


224 


PRIMULA    VEEIS. 


Chap.  VI. 


Table  XCIV. 

Primula  veris  (equal-styled,  red-flowered  variety). 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilis "d  Plants. 

Height  of 

tallest 

Flower-stem 

in  inches. 

No.  of 
Flower- 
stems. 

No.  of  good 
Capsul  s. 

Height  of 

tallest 

Flower-stem 

in  indies. 

No.  of 
Flower- 
stems. 

No.  of  good 
Capsules. 

I. 

10 

14 

163 

H 

6 

6 

II. 

R4 

I  Several, 
12             not 
'  counted. 

5 

2 

0 

III. 

74 

•  S 

7       |  '     43 

log 

5 

26 

Totals. 

26-0 

33       |     206 

22-0 

13 

32 

The  average  height  of  the  three  tallest  flower-stems  on  the 
crossed  plants  is  8  ■  66  inches,  and  that  of  the  three  on  the 
self-fertilised  plants  7  •  33  inches ;  or  as  100  to  85. 

All  the  crossed  plants  together  produced  thirty-three  flower- 
stems,  whilst  the  self-fertilised  bore  only  thirteen.  The  number 
of  the  capsules  were  counted  only  on  the  plants  in  Pots  I.  and  III., 
for  the  self-fertilised  plants  in  Pot  II.  produced  none ;  therefore 
those  on  the  crossed  plants  on  the  opposite  side  were  not 
counted.  Capsules  not  containing  any  good  seeds  were  rejected. 
The  crossed  plants  in  the  above  two  pots  produced  206,  and  the 
self-fertilised  in  the  same  pots  only  32  capsules;  or  as  100 
to  15.  Judging  from  the  previous  generations,  the  extreme 
unproductiveness  of  the  self-fertilised  plants  in  this  experiment 
was  wholly  due  to  their  having  been  subjected  to  unfavourable 
conditions,  and  to  severe  competition  with  the  crossed  plants ; 
for  had  they  grown  separately  in  good  soil,  it  is  almost  certain 
that  they  would  have  produced  a  large  number  of  capsules. 
The  seeds  were  counted  in  twenty  capsules  from  the  crossed 
plants,  and  they  averaged  24 '75;  whilst  in  twenty  capsules 
from  the  self-fertilised  plants  the  average  was  17*65;  or  as 
100  to  71.  Moreover,  the  seeds  from  the  self-fertilised  plants 
were  not  nearly  so  fine  as  those  from  the  crossed  plants.  If 
we  consider  together  the  number  of  capsules  produced  and 
the  average  number  of  contained  seeds,  the  fertility  of  the 
crossed  plants  to  the  self-fertilised  plants  was  as  100  to  11. 


Chap.  VI.  PKIMULA  SINENSIS.  225 

We  thus  see  what  a  great  effect,  as  far  as  fertility  is  concerned, 
was  produced  by  a  cross  between  the  two  varieties,  which  had 
been  long  exposed  to  different  conditions,  in  comparison  with 
self-fertilisation ;  the  fertilisation  having  been  in  both  cases  of 
the  legitimate-order. 

Peimula  sinensis. 

As  the  Chinese  primrose  is  a  heterostyled  or  dimorphic  plant, 
like  the  common  cowslip,  it  might  have  been  expected  that  the 
flowers  of  both  forms  when  illegitimately  fertilised  with  their 
own  pollen  or  with  that  from  flowers  on  another  plant  of  the 
same  form,  would  have  yielded  less  seed  than  the  legitimately 
crossed  flowers;  and  that  the  seedlings  raised  from  illegiti- 
mately self-fertilised  seeds  would  have  been  somewhat  dwarfed 
and  less  fertile,  in  comparison  with  the  seedlings  from  legiti- 
mately crossed  seeds.  This  holds  good  in  relation  to  the  fer- 
tility of  the  flowers ;  but  to  my  surprise  there  was  no  difference 
in  growth  between  the  offspring  from  a  legitimate  union  between 
two  distinct  plants,  and  from  an  illegitimate  union  whether 
between  the  flowers  on  the  same  plant,  or  between  distinct  plants 
of  the  same  form.  But  I  have  shown,  in  the  paper  before  referred 
to,  that  in  England  this  plant  is  in  an  abnormal  Condition, 
such  as,  judging  from  analogous  cases,  would  tend  to  render  a 
cross  between  two  individuals  of  no  benefit  to  the  offspring. 
Our  plants  have  been  commonly  raised  from  self-fertilised 
seeds ;  and  the  seedlings  have  generally  been  subjected  to  nearly 
uniform  conditions  in  pots  in  greenhouses.  Moreover,  many  of 
the  plants  are  now  varying  and  changing  their  character,  so  as 
to  become  in  a  greater  or  less  degree  equal-styled,  and  in  con- 
sequence highly  self-fertile.  From  the  analogy  of  P.  veris  there 
can  hardly  be  a  doubt  that  if  a  plant  of  P.  sinensis  could  have 
been  procured  direct  from  China,  and  if  it  had  been  crossed 
with  one  of  our  English  varieties,  the  offspring  would  have 
shown  wonderful  superiority  in  height  and  fertility  (though 
probably  not  in  the  beauty  of  their  flowers)  over  our  ordinary 
plants. 

My  first  experiment  consisted  in  fertilising  many  flowers  on 
long-styled  and  short-styled  plants  with  their  own  pollen,  and 
other  flowers  on  the  same  plants  with  pollen  taken  from  distinct 
plants  belonging  to  the  same  form ;  so  that  all  the  unions  were 
illegitimate.    There  was  no  uniform  and  marked  difference  in 


226  PRIMULA   SINENSIS.  Chap.  VI. 

the  number  of  seeds  obtained  from  these  two  modes  of  self-fer- 
tilisation, both  of  which  were  illegitimate.  The  two  lots  of  seeds 
from  both  forms  were  sown  thickly  on  opposite  sides  of  four  pots, 
and  numerous  plants  thus  raised.  But  there  was  no  difference 
in  their  growth,  excepting  in  one  pot,  in  which  the  offspring 
from  the  illegitimate  -union  of  two  long-styled  plants  exceeded 
in  a  decided  manner  in  height  the  offspring  of  flowers  on  the 
same  plants  fertilised  with  their  own  pollen.  But  in  all  four 
pots  the  plants  raised  from  the  union  of  distinct  plants  belonging 
to  the  same  form,  flowered  before  the  offspring  from  the  self- 
fertilised  flowers. 

Some  long-styled  and  short-styled  plants  were  now  raised  from 
purchased  seeds,  and  flowers  on  both  forms  were  legitimately 
crossed  with  pollen  from  a  distinct  plant ;  and  other  flowers  on 
both  forms  were  illegitimately  fertilised  with  pollen  from  the 
flowers  on  the  same  plant.  The  seeds  were  sown  on  opposite  sides 
of  Pots  I.  to  IV.  in  the  following  table  (XCV.) ;  a  single  plant 
being  left  on  each  side.  Several  flowers  on  the  illegitimate  long- 
styled  and  short-styled  plants  described  in  the  last  paragraph, 
were  also  legitimately  and  illegitimately  fertilised  in  the  manner 
just  described,  and  their  seeds  were  sown  in  Pots  V.  to  VIII.  in 
the  same  table.  As  the  two  sets  of  seedlings  did  not  differ  in 
any  essential  manner,  their  measurements  are  given  in  a  single 
table.  I  should  add  that  the  legitimate  unions  in  both  cases 
yielded,  as  might  have  been  expected,  many  more  seeds  than  the 
illegitimate  unions.  The  seedlings  whilst  half-grown  presented 
no  difference  in  height  on  the  two  sides  of  the  several  pots. 
When  fully  grown  they  were  measured  to  the  tips  of  their 
longest  leaves,  and  the  result  is  given  in  Table  XCV. 

In  six  out  of  the  eight  pots  the  legitimately  crossed  plants 
exceeded  in  height  by  a  trifle  the  illegitimately  self-fertilised 
plants ;  but  the  latter  exceeded  the  former  in  two  of  the  pots  in  a 
more  strongly  marked  manner.  The  average  height  of  the  eight 
legitimately  crossed  plants  is  9  •  01,  and  that  of  the  eight  illegi- 
timately self-fertilised  9*03  inches;  or  as  100  to  100 ■  2.  The 
plants  on  the  opposite  sides  produced,  as  far  as  could  be  judged 
by  the  eye,  an  equal  number  of  flowers.  I  did  not  count  the  cap- 
sules or  the  seeds  produced  by  them ;  but  undoubtedly,  judging 
from  many  previous  observations,  the  plants  derived  from  the 
legitimately  crossed  seeds  would  have  been  considerably  more 
fertile  than  those  from  the  illegitimately  self-fertilised  seeds. 
The  crossed  plants,  as  in  the  previous  case,  flowered  before  the 


Ohap.  VI. 


PKIMULA   SINENSIS. 


227 


Table  XCV. 

Primula  sinensis. 


Tin    of  Pnt               '      PlantS  fr0m  leg5ti" 
JNO.  01  ±-0t.             |  mately  crossed  Seeds. 

Plants  from  illegiti- 
mately self-fertilised 
Seeds. 

I. 

From  short-styled 
mother. 

Inches. 
°g 

Inches. 
8 

II. 

From  short-styled 
mother. 

74 
•  s 

»f 

III. 

From  long-styled 

mother. 

9f 

n 

IV. 

From  long-styled 

mother. 

8§ 

8§ 

V. 

From  illegitimate 

short-styled 

mother. 

91 

9 

VI. 

From  illegitimate 

short-styled 

mother. 

91 

H 

VII. 

From  illegitimate 
long-styled  mother. 

8| 

98 

VIII. 
From  illegitimate 
long-styled  mother. 

lOf 

10 
72-25 

Total  in  inches. 

72-13 

Felf-fertilised  plants  in  all  the  pots  except  in  Pot  II.,  in  which  the 
two  sides  flowered  simultaneously;  and  this  early  flowering 
may,  perhaps,  be  considered  as  an  advantage. 


228  FAGOPYRUM  ESCULENTUM.  Chap.  Vt. 

XXVII.  POLYGONE^.— Fagopyrum  esculentum. 

This  plant  was  discovered  by  Hildebrand  to  be  heterostyled, 
that  is,  to  present,  like  the  species  of  Primula,  a  long- styled  and  a 
short-styled  form,  which  are  adapted  for  reciprocal  fertilisation. 
Therefore  the  following  comparison  of  the  growth  of  the  crossed 
and  self-fertilised  seedlings  is  not  fair,  for  we  do  not  know 
whether  the  difference  in  their  heights  may  not  be  wholly  due  to 
the  illegitimate  fertilisation  of  the  self-fertilised  flowers. 

I  obtained  seeds  by  legitimately  crossing  flowers  on  long-styled 
and  short-styled  plants,  and  by  fertilising  other  flowers  on  both 
forms  with  pollen  from  the  same  plant.  Eather  more  seeds  were 
obtained  by  the  former  than  by  the  latter  process ;  and  the 
legitimately  crossed  seeds  were  heavier  than  an  equal  number 
of  the  illegitimately  self-fertilised  seeds,  in  the  ratio  of  100  to  82. 
Crossed  and  self-fertilised  seeds  from  the  short-styled  parents, 
after  germinating  on  sand,  were  planted  in  pairs  on  the  opposite 
sides  of  a  large  pot ;  and  two  similar  lots  of  seeds  from  long- 
styled  parents  were  planted  in  a  like  manner  on  the  opposite 
sides  of  two  other  pots.  In  all  three  pots  the  legitimately  crossed 
seedlings,  when  a  few  inches  in  height,  were  taller  than  the  self- 
fertilised  ;  and  in  all  three  pots  they  flowered  before  them  by  one 
or  two  days.  When  fully  grown  they  were  all  cut  down  close 
to  the  ground,  and  as  I  was  pressed  for  time,  they  were  placed 
in  a  long  row,  the  cut  end  of  one  plant  touching  the  tip  of 
another,  and  the  total  length  of  the  legitimately  crossed  plants 
was  47  ft.  7  in.,  and  of  the  illegitimately  self-fertilised  plants 
32  ft.  8  in.  Therefore  the  average  height  of  the  fifteen  crossed 
plants  in  all  three  pots  was  38  •  06  inches,  and  that  of  the  fifteen 
self-fertilised  plants  26  *  13  inches ;  or  as  100  to  69. 

XXVIII.  CHENOPODIACE^E.— Beta  vulgaris. 

A  single  plant,  no  others  growing  in  the  same  garden,  was 
left  to  fertilise  itself,  and  the  self-fertilised  seeds  were  collected. 
Seeds  were  also  collected  from  a  plant  growing  in  the  midst  of  a 
large  bed  in  another  garden ;  and  as  the  incoherent  pollen  is 
abundant,  the  seeds  of  this  plant  will  almost  certainly  have  been 
the  product  of  a  cross  between  distinct  plants  by  means  of  the 
wind.  Some  of  the  two  lots  of  seeds  were  sown  on  the  opposite 
sides  of  two  very  large  pots ;  and  the  young  seedlings  were 
thinned,  so  that  an  equal  but  considerable  number  was  left  on 
the  two  sides.     These  plants  were  thus  subjected  to  very  severo 


Chap.  VI. 


BETA   VULGARIS. 


229 


competition,  as  well  as  to  poor  conditions.  The  remaining  seeds 
were  sown  out  of  doors  in  good  soil  in  two  long  and  not  closely 
adjoining  rows,  so  that  these  seedlings  were  placed  under  favour- 
able conditions,  and  were  not  subjected  to  any  mutual  com- 
petition. The  self-fertilised  seeds  in  the  open  ground  came  up 
very  badly ;  and  on  removing  the  soil  in  two  or  three  places,  it 
was  found  that  many  had  sprouted  under  ground  and  had 
then  died.  No  such  case  had  been  observed  before.  Owing  to 
the  large  number  of  seedlings  which  thus  perished,  the  sur- 
viving self-fertilised  plants  grew  thinly  in  the  row,  and  thus  had 
an  advantage  over  the  crossed  plants,  which  grew  very  thickly 
in  the  other  row.  The  young  plants  in  the  two  rows  were  pro- 
tected by  a  little  straw  during  the  winter,  and  those  in  the  two 
large  pots  were  placed  in  the  greenhouse. 

There  was  no  difference  between  the  two  lots  in  the  pots  until 
the  ensuing  spring,  when  they  had  grown  a  little,  and  then  some 
of  the  crossed  plants  were  finer  and  taller  than  any  of  the  self- 
fertilised.  When  in  full  flower  their  stems  were  measured,  and 
the  measurements  are  given  in  the  following  table  : — 

Table  XCVI. 
Beta  vulgaris. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
34f 
30 
33| 
34 1 

Inches. 
36 
20J 
32 1 
32 

II. 

42  j{ 
33  \ 
31 1 
33 

42J 

26 1 
29§ 
20§ 

Total  in  inches. 

272-75 

238-50 

The  average  height  of  the  eight  crossed  plants  is  here 
34*09,  and  that  of  the  eight  self-fertilised  plants  29*81 ;  or  as 
100  to  87. 

With  respect  to  the  plants  in  the  open  ground,  each  long  row 
was  divided  into  half,  so  as  to  diminish  the  chance  of  any 
accidental  advantage  in  one  part  of  either  row;  and  the  four 
tallest  plants  in  the  two  halves  of  the  two  rows  were  carefully 


230  CANNA  WARSCEWICZI.  Chap.  VI. 

selected  and  measured.  The  eight  tallest  crossed  plants  averaged 
80-92,  and  the  eight  tallest  self-fertilised  30  "7  inches  in  height, 
or  as  100  to  99 ;  so  that  they  were  practically  equal.  But  we 
should  bear  in  mind  that  the  trial  was  not  quite  fair,  as  the 
self-fertilised  plants  had  a  great  advantage  over  the  crossed 
in  being  much  less  crowded  in  their  own  row,  owing  to  the 
large  number  of  seeds  which  had  perished  under  ground  after 
sprouting.  Nor  were  the  lots  in  the  two  rows  subjected  to  any 
mutual  competition. 

XXIX.  CANNACE^].— Canna  waescewiozi. 

In  most  or  all  the  species  belonging  to  this  genus,  the  pollen 
is  shed  before  the  flower  expands,  and  adheres  in  a  mass  to  the 
foliaceous  pistil  close  beneath  the  stigmatic  surface.  As  the 
edge  of  this  mass  generally  touches  the  edge  of  the  stigma,  and 
as  it  was  ascertained  by  trials  purposely  made  that  a  very  few 
pollen-grains  suffice  for  fertilisation,  the  present  species  and 
probably  all  the  others  of  the  genus  are  highly  self-fertile. 
Exceptions  occasionally  occur  in  which,  from  the  stamen  being 
slightly  shorter  than  usual,  the  pollen  is  deposited  a  little  beneath 
the  stigmatic  surface,  and  such  flowers  drop  off  unimpreg- 
nated  unless  they  are  artificially  fertilised.  Sometimes,  though 
rarely,  the  stamen  is  a  little  longer  than  usual,  and  then  the 
whole  stigmatic  surface  gets  thickly  covered  with  pollen.  As 
some  pollen  is  generally  deposited  in  contact  with  the  edge  of 
the  stigma,  certain  authors  have  concluded  that  the  flowers  are 
invariably  self-fertilised.  This  is  an  extraordinary  conclusion, 
for  it  implies  that  a  great  amount  of  pollen  is  produced  for  no 
purpose.  On  this  view,  also,  the  large  size  of  the  stigmatic 
surface  is  an  unintelligible  feature  in  the  structure  of  the  flower, 
as  well  as  the  relative  position  of  all  the  parts,  which  is  such 
that  when  insects  visit  the  flowers  to  suck  the  copious  nectar, 
they  cannot  fail  to  carry  pollen  from  one  flower  to  another.  * 


*  Del  pino  has  described  (' Bot.  are  fertilised  in  the  bud,  and  that 

Zeitung,'  1867,  p.  277,  and '  Scien-  self-fertilisation  is  inevitable.     I 

tine  Opinion,'  1870,  p.   135)  the  presume  that  they  were  misled  by 

b tract  are   of  the  flowers  in  this  the  pollen  being  deposited  at  a 

genus,  but  he  was   mistaken  in  very  early  period  on  the  pistil :  see 

thinking  that  self- fertilisation  is  'Journal  of  Linn.  Soc.  Bot.' vol. 

impossible,  at  least  in  the  case  of  x.    p.    55,   and    '  Variability   des 

the  present  species.  Dr.  Dickie  and  Especes,'  1868,  p.  158. 
Prof".  Faivre  state  that  the  flowers 


Chai>.  VI.  CANNA   WAESCEWICZI.  .         231 

According  to  Delpino,  bees  eagerly  visit  the  flowers  in  North 
Italy,  hut  I  have  never  seen  any  insect  visiting  the  flowers  of  the 
present  species  in  my  hothouse,  although  many  plants  grew 
there  during  several  years.  Nevertheless  these  plants  produced 
plenty  of  seed,  as  they  likewise  did  when  covered  by  a  net;  they 
are  therefore  fully  capable  of  self- fertilisation,  and  have  probably 
been  self-fertilised  in  this  country  for  many  generations.  As 
they  are  cultivated  in  pots,  and  are  not  exposed  to  competition 
with  surrounding  plants,  they  have  also  been  subjected  for  a 
considerable  time  to  somewhat  uniform  conditions.  This,  there- 
fore, is  a  case  exactly  parallel  with  that  of  the  common  pea,  in 
which  we  have  no  right  to  expect  much  or  any  good  from 
intercrossing  plants  thus  descended  and  thus  treated;  and 
no  good  did  follow,  excepting  that  the  cross-fertilised  flowers 
yielded  rather  more  seeds  than  the  self-fertilised.  This  species 
was  one  of  the  earlier  ones  on  which  I  experimented,  and  as  I 
had  not  then  raised  any  self-fertilised  plants  for  several  successive 
generations  under  uniform  conditions,  I  did  not  know  or  even 
suspect  that  such  treatment  would  interfere  with  the  advantages 
to  be  gained  from  a  cross.  I  was  therefore  much  surprised  at 
the  crossed  plants  not  growing  more  vigorously  than  the  self- 
fertilised,  and  a  large  number  of  plants  were  raised,  notwith- 
standing that  the  present  species  is  an  extremely  troublesome 
one  to  experiment  on.  The  seeds,  even  those  which  have  been 
long  soaked  in  water,  will  not  germinate  well  on  bare  sand ;  and 
those  that  were  sown  in  pots  (which  plan  I  was  forced  to  follow) 
germinated  at  very  unequal  intervals  of  time;  so  that  it  was 
difficult  to  get  pairs  of  the  same  exact  age,  and  many  seedlings 
had  to  be  pulled  up  and  thrown  away.  My  experiments  were 
continued  during  three  successive  generations ;  and  in  each 
generation  the  self-fertilised  plants  were  again  self-fertilised, 
their  early  progenitors  in  this  country  having  probably  been  self- 
fertilised  for  many  previous  generations.  In  each  generation, 
also,  the  crossed  plants  were  fertilised  with  pollen  from  another 
crossed  plant. 

Of  the  flowers  which  were  crossed  in  the  three  generations, 
taken  together,  a  rather  larger  proportion  yielded  capsules  than 
did  those  which  were  self -fertilised.  The  seeds  were  counted  in 
forty-seven  capsules  from  the  crossed  flowers,  and  they  con- 
tained on  an  average  9 "  95  seeds ;  whereas  forty-eight  capsules 
from  the  self-fertilised  flowers  contained  on  an  average  8*45 
seeds ;  or  as  100  to  85.  The  seeds  from  the  crossed  flowers  were 
11 


232  CANNA  WARSCEWICZI.  Chap.  VL 

not  heavier,  on  the  contrary  a  little  lighter,  than  those  from  the 
self-fertilised  flowers,  as  was  thrice  ascertained.  On  one  occasion 
I  weighed  200  of  the  crossed  and  106  of  the  self-fertilised  seeds, 
and  the  relative  weight  of  an  equal  number  was  as  100  for  the 
crossed  to  101  "5  for  the  self-fertilised.  With  other  plants,  when 
the  seeds  from  the  self-fertilised  flowers  were  heavier  than  those 
from  the  crossed  flowers,  this  appeared  to  be  due  generally 
to  fewer  having  been  produced  by  the  self-fertilised  flowers,  and 
to  their  having  been  in  consequence  better  nourished.  But  in 
the  present  instance  the  seeds  from  the  crossed  capsules  were 
separated  into  two  lots, — namely,  those  from  the  capsules  con- 
taining over  fourteen  seeds,  and  those  from  capsules  containing 
under  fourteen  seeds,  and  the  seeds  from  the  more  productive 
capsules  were  the  heavier  of  the  two ;  so  that  the  above  explana- 
tion here  fails. 

As  pollen  is  deposited  at  a  very  early  age  on  the  pistil,  gene- 
rally in  contact  with  the  stigma,  some  flowers  whilst  still  in 
bud  were  castrated  for  my  first  experiment,  and  were  afterwards 
fertilised  with  pollen  from  a  distinct  plant.  Other  flowers  were 
fertilised  with  their  own  pollen.  From  the  seeds  thus  ob- 
tained, I  succeeded  in  rearing  only  three  pairs  of  plants  of  equal 
age.  The  three  crossed  plants  averaged  32  "79  inches,  and 
the  three  self-fertilised  32-08  inches  in  height;  so  that  they 
were  nearly  equal,  the  crossed  having  a  slight  advantage.  As 
the  same  result  followed  in  all  three  generations,  it  would  be 
superfluous  to  give  the  heights  of  all  the  plants,  and  I  will  give 
only  the  averages. 

In  order  to  raise  crossed  and  self-fertilised  plants  of  the  second 
generation,  some  flowers  on  the  above  crossed  plants  were  crossed 
within  twenty-four  hours  after  they  had  expanded  with  pollen 
from  a  distinct  plant ;  and  this  interval  would  probably  not  be  too 
great  to  allow  of  cross-fertilisation  being  effectual.  Some  flowers 
on  the  self -fertilised  plants  of  the  last  generation  were  also  self- 
fertilised.  From  these  two  lots  of  seeds,  ten  crossed  and  twelve 
self-fertilised  plants  of  equal  ages  were  raised ;  and  these  were 
measured  when  fully  grown.  The  crossed  averaged  36  ■  98,  and 
the  self-fertilised  averaged  37 "42  inches  in  height;  so  that  here 
again  the  two  lots  were  nearly  equal ;  but  the  self-fertilised  had 
a  slight  advantage. 

In  order  to  raise  plants  of  the  third  generation,  a  better  plan 
was  followed,  and  flowers  on  the  crossed  plants  of  the  second 
generation  were  selected  in  which  the  stamens  were  too  short  to 


Chap.  VI.  ZEA  MATS.  233 

reach  the  stigmas,  so  that  they  could  not  possibly  have  been 
self-fertilised.  These  flowers  were  crossed  with  pollen  from  a 
distinct  plant.  Flowers  on  the  self-fertilised  plants  of  the  second 
generation  were  again  self-fertilised.  From  the  two  lots  of  seeds 
thus  obtained,  twenty-one  crossed  and  nineteen  self-fertilised 
plants  of  equal  age,  and  forming  the  third  generation,  were  raised 
in  fourteen  large  pots.  They  were  measured  when  fully  grown, 
and  by  an  odd  chance  the  average  height  of  the  two  lots  was 
exactly  the  same, namely,  35*96  inches;  so  that  neither  side  had 
the  least  advantage  over  the  other.  To  test  this  result,  all  the 
plants  on  both  sides  in  ten  out  of  the  above  fourteen  pots  were 
cut  down  after  they  had  flowered,  and  in  the  ensuing  year  the 
stems  were  again  measured;  and  now  the  crossed  plants  ex- 
ceeded by  a  little  (viz..  1*7  inches)  the  self-fertilised.  They  were 
again  cut  down,  and  on  their  flowering  for  the  third  time,  the 
self-fertilised  plants  had  a  slight  advantage  (viz.,  1  ■  54  inches) 
over  the  crossed.  Hence  the  result  arrived  at  with  these  plants 
during  the  previous  trials  was  confirmed,  namely,  that  neither 
lot  had  any  decided  advantage  over  the  other.  It  may,  however, 
be  worth  mentioning  that  the  self-fertilised  plants  showed  some 
tendency  to  flower  before  the  crossed  plants :  this  occurred  with 
all  three  pairs  of  the  first  generation ;  and  with  the  cut  down 
plants  of  the  third  generation,  a  self-fertilised  plant  flowered 
first  in  nine  out  of  the  twelve  pots,  whilst  in  the  remaining  three 
pots  a  crossed  plant  flowered  first. 

If  we  consider  all  the  plants  of  the  three  generations  taken 
together,  the  thirty-four  crossed  plants  average  35  ■  98,  and  the 
thirty-four  self-fertilised  plants  36 '39  inches  in  height:  or  as 
100  to  101.  We  may  therefore  conclude  that  the  two  lots 
possessed  equal  powers  of  growth ;  and  this  I  believe  to  be  the 
result  of  long-continued  self-fertilisation,  together  with  exposure 
to  similar  conditions  in  each  generation,  so  that  all  the  indivi- 
duals had  acquired  a  closely  similar  constitution. 

XXX.  GEAMINACE^I.— Zea  mats. 

This  plant  is  monoecious,  and  was  selected  for  trial  on  this  ac- 
count, no  other  such  plant  having  been  experimented  on.*    It  is 


*     Hildebrand     remarks    that  male  flowers  standing  above  the 

this  species  seems  at  first   sight  female  flowers ;  but  practically  it 

adapted  to  be  fertilised  by  pollen  must  generally   be   fertilised   by 

from  the  same  ojant,  owing  to  the  pollen  from  another  plant,  as  the 


234 


ZEA   MAYS. 


Chap.  VI. 


also  anemophilous,  or  is  fertilised  by  the  wind ;  and  of  such  plants 
only  the  common  beet  had  been  tried.  Some  plants  were  raised 
in  tbe  greenhouse,  and  were  crossed  with  pollen  taken  from  a 
distinct  plant ;  and  a  single  plant,  growing  quite  separately  in  a 
different  part  of  the  house,  was  allowed  to  fertilise  itself  spon- 
taneously. The  seeds  thus  obtained  were  placed  on  damp  sand, 
and  as  they  germinated  in  pairs  of  equal  age  were  planted  on 
tho  opposite  sides  of  four  very  large  pots;  nevertheless  they 
were  considerably  crowded.  The  pots  were  kept  in  the  hothouse. 
The  plants  were  first  measured  to  the  tips  of  their  leaves  when 
only  between  1  and  2  feet  in  height,  as  shown  in  the  following 
table : — 

Table  XCVII. 
Zea  mays. 


No.  of  Pot. 

Crossed  Plants. 

Self-fertilised  Plants. 

I. 

Inches. 
23 1 
12 
21 

Inches. 
17| 

20  a 

20 

IL 

22 

193 

212 

20 

18| 

18! 

III. 

22 1 

20f 
1S§ 
21| 
23 1 

18f 
15§ 

16| 

18 
16 1 

IV. 

21 
22  J 
23 
12 

18 
12 1 
15| 
18 

Total  in  inches. 

302-88 

263-63 

The  fifteen  crossed  plants  here  average  20  "19,  and  the  nfteen 
self-fertilised  plants  17*57  inches  in  height;  or  as  100  to  87. 
Mr.  Galton  made  a  graphical  representation,  in  accordance  with 
the  method  described  in  the  introductory  chapter,  of  the  above 


male  flowers  usually  shed   their      K.     Akad.' 
pollen  before  the  female  flowers       p.  743. 
arg   mature :   '  Monatsberickt  der 


Berlin,    Oct.    1872, 


Chap.  VI.  PHALAKIS   CANAEIENSIS.  235 

measurements,  and  adds  the  words  "  very  good  "  to  the  curves 
thus  formed. 

Shortly  afterwards  one  of  the  crossed  plants  in  Pot  I.  died ; 
another  became  much  diseased  and  stunted ;  and  the  third  never 
grew  to  its  full  height.  They  seemed  to  have  been  all  injured, 
probably  by  some  larva  gnawing  their  roots.  Therefore  all 
the  plants  on  both  sides  of  this  pot  were  rejected  in  the  subse- 
quent measurements.  When  the  plants  were  fully  grown  they 
were  again  measured  to  the  tips  of  the  highest  leaves,  and  the 
eleven  crossed  plants  now  averaged  68*1,  and  the  eleven  self- 
fertilised  plants  62  ■  34  inches  in  height ;  or  as  100  to  91.  In  all 
four  pots  a  crossed  plant  flowered  before  any  one  of  the  self-fer- 
tilised ;  but  three  of  the  plants  did  not  flower  at  all.  Those  that 
flowered  were  also  measured  to  the  summits  of  the  male  flowers : 
the  ten  crossed  plants  averaged  66*51,  and  the  nine  self-fertilised 
plants  61 "  59  inches  in  height ;  or  as  100  to  93. 

A  large  number  of  the  same  crossed  and  self-fertilised  seeds 
were  sown  in  the  middle  of  the  summer  in  the  open  ground  in 
two  long  rows.  Very  much  fewer  of  the  self-fertilised  than  of 
the  crossed  plants  produced  flowers ;  but  those  that  did  flower, 
flowered  almost  simultaneously.  When  fully  grown  the  ten 
tallest  plants  in  each  row  were  selected  and  measured  to  the 
tips  of  their  highest  leaves,  as  well  as  to  the  summits  of  their 
male  flowers.  The  crossed  averaged  to  the  tips  of  their  leaves 
54  inches  in  height,  and  the  self-fertilised  44 '65,  or  as  100 
to  83;  and  to  the  summits  of  their  male  flowers,  53*96  and 
43  •  45  inches ;  or  as  100  to  80. 

Phalakis  canaeiensis. 

Hildebrand  has  shown  in  the  paper  referred  to  under  the 
last  species,  that  this  hermaphrodite  grass  is  better  adapted 
for  cross-fertilisation  than  for  self-fertilisation.  Several  plants 
were  raised  in  the  greenhouse  close  together,  and  their  flowers 
were  mutually  intercrossed.  Pollen  from  a  single  plant  growing 
quite  separately  was  collected  and  placed  on  the  stigmas  of  the 
same  plant.  The  seeds  thus  produced  were  self-fertilised,  for 
they  were  fertilised  with  pollen  from  the  same  plant,  but  it  will 
have  been  a  mere  chance  whether  with  pollen  from  the  same 
flowers.  Both  lots  of  seeds,  after  germinating  on  sand,  were 
planted  in  pairs  on  the  opposite  sides  of  four  pots,  which  wero 
kept  in  the  greenhouse.    When  the  plants  were  a  little  over  a 


236 


PHALAEI3   CANARIENSIS. 


Chap.  VI. 


foot  in  height  they  were  measured,  and  the  crossed  plants 
averaged  13  ■  38,  and  the  self-fertilised  12 "  29  inches  in  height ; 
or  as  100  to  92. 

When  in  full  flower  they  were  again  measured  to  the  ex- 
tremities of  their  culms,  as  shown  in  the  following  table : — ■ 


Table  XCVIII. 

Phalaris  canariensis. 


No.  of  Pot.                Crossed  Plants. 

i 

Self-fertilised  Plants. 

Inches. 
I.                               42 1 
39  j 

Inches. 
41  § 
45 1 

II. 

37 

49 1 

29 

37 

31  f 
37 1 
42 1 
34? 

in. 

37 1 
35 | 

43 

28 
28 
34 

IV. 

40  § 
37 

35a- 
34$ 

Total  in  inches. 

428-00 

392-63 

The  eleven  crossed  plants  now  averaged  38 '9,  and  the  eleven 
self-fertilised  plants  35  ■  69  inches  in  height ;  or  as  100  to  92, 
which  is  the  same  ratio  as  before.  Differently  to  what  occurred 
with  the  maize,  the  crossed  plants  did  not  flower  before  the  self- 
fertilised;  and  though  both  lots  flowered  very  poorly  from 
having  been  kept  in  pots  in  the  greenhouse,  yet  the  self-fertilised 
plants  produced  twenty-eight  flower-heads,  whilst  the  crossed 
produced  only  twenty ! 

Two  long  rows  of  the  same  seeds  were  sown  out  of  doors,  and 
care  was  taken  that  they  were  sown  in  nearly  equal  number ; 
but  a  far  greater  number  of  the  crossed  than  of  the  self-fertilised 
seeds  yielded  plants.  The  self-fertilised  plants  were  in  con- 
sequence not  so  much  crowded  as  the  crossed,  and  thus  had  an 
advantage  over  them.  When  in  full  flower,  the  twelve  tallest 
plants  were  carefully  selected  from  both  rows  and  measured, 
as  shown  in  the  following  table : — 


Chap.  VI. 


PHALAEIS   CANAEIENSIS. 


237 


Table  XCIX. 
Phdlaris  canarien&is  (growing  in  the  open  ground). 


Crossed  Plants,  twelve 

Self-fertilised  Plants, 

tallest. 

twelve  tailest. 

Inches. 

Inches. 

34' 

35§ 

351 

3U 

36 

33 

35 1 

32 

35 1 

si  § 

36| 

36 

36| 

33 

38 1 

32 

36§ 

35| 

35| 

33| 

34  S 

34 1 

34f 

35 

Total  in  7 

inches.)   *-»   o 

402-0 

The  twelve  crossed  plants  here  average  35  '78,  and  the  twelve 
self-fertilised  33 '  5  inches  in  height ;  or  as  100  to  93.  Tn  this 
case  the  crossed  plants  flowered  rather  before  the  self-fertilised, 
and  thus  differed  from  those  growing  in  the  pots. 


2SS  SUMMARY   OF   MEASUREMENTS.  Chat.  711. 


CHAPTER  VII. 

Summary  of  the  Heights  and  Weights  of  the  Crossed  and 
Self-fertilised  Plants. 

Number  of  species  and  plants  measured — Tables  given — Preliminary 
remarks  on  the  offspring  of  plants  crossed  by  a  fresh  stock— Thirteen 
cases  specially  considered — The  effects  of  crossing  a  self-fertilised 
plant  either  by  another  self-fertilised  plant  or  by  an  intercrossed  plant 
of  the  old  stock — Summary  of  the  results — Preliminary  remarks  on 
the  crossed  and  self-fertilised  plants  of  the  same  stock— The  twenty- 
six  exceptional  cases  considered,  in  which  the  crossed  plants  did  not 
exceed  greatly  in  height  the  self-fertilised — Most  of  these  cases 
shown  not  to  be  real  exceptions  to  the  rule  that  cross-fertilisation 
is  beneficial— Summary  of  results — Relative  weights  of  the  crossed 
and  self-fertilised  plants. 

The  details  which  have  been  given  under  the  head 
of  each  species  are  so  numerous  and  so  intricate,  that 
it  is  necessary  to  tabulate  the  results.  In  Table  A,  the 
number  of  plants  of  each  kind  which  were  raised  from 
a  cross  between  two  individuals  of  the  same  stock  and 
from  self-fertilised  seeds,  together  with  their  mean 
or  average  heights,  are  given.  In  the  right-hand 
column,  the  mean  height  of  the  crossed  to  that  of 
the  self-fertilised  plants,  the  former  being  taken  as 
100,  is  shown.  To  make  this  clear,  it  may  be  ad- 
visable to  give  an  example.  In  the  first  generation  of 
Ipomoea,  six  plants  derived  from  a  cross  between  two 
plants  were  measured,  and  their  mean  height  is  86  ■  00 
inches ;  six  plants  derived  from  flowers  on  the  same 
parent-plant  fertilised  with  their  own  pollen  were 
measured,   and  their  mean  height  is  65*66   inches. 


Chap.  VII.         SUMMAKY   OF   MEASUREMENTS.  239 

From  this  it  follows,  as  shown  in  the  right-hand 
column,  that  if  the  mean  height  of  the  crossed  plants 
be  taken  as  100,  that  of  the  self-fertilised  plants  is  76. 
The  same  plan  is  followed  with  all  the  other  species. 

The  crossed  and  self-fertilised  plants  were  generally 
grown  in  pots  in  competition  with  one  another,  and 
always  under  as  closely  similar  conditions  as  could 
be  attained.  They  were,  however,  sometimes  grown  in 
separate  rows  in  the  open  ground.  With  several  of 
the  species,  the  crossed  plants  were  again  crossed,  and 
the  self-fertilised  plants  again  self-fertilised,  and  thus 
successive  generations  were  raised  and  measured,  as 
may  be  seen  in  Table  A.  Owing  to  this  manner  of 
proceeding,  the  crossed  plants  became  in  the  later 
generations  more  or  less  closely  inter-related. 

In  Table  B  the  relative  weights  of  the  crossed  and 
self-fertilised  plants,  after  they  had  flowered  and  had 
been  cut  down,  are  given  in  the  few  cases  in  which 
they  were  ascertained.  The  results  are,  I  think,  more 
striking  and  of  greater  value  as  evidence  of  constitu- 
tional vigour  than  those  deduced  from  the  relative 
heights  of  the  plants. 

The  most  important  table  is  that  of  C,  as  it  includes 
the  relative  heights,  weights,  and  fertility  of  plants 
raised  from  parents  crossed  by  a  fresh  stock  (that  is,  by 
non-related  plants  grown  under  different  conditions), 
or  by  a  distinct  sub-variety,  in  comparison  with  self- 
fertilised  plants,  or  in  a  few  cases  with  plants  of  the 
same  old  stock  intercrossed  during  several  generations. 
The  relative  fertility  of  the  plants  in  this  and  the 
other  tables  will  be  more  fully  considered  in  a  future 
chapter. 


240 


SUMMARY   OF   MEASUREMENTS. 


Chap.  VIL 


Table  A. — Relative  Heights  of  Plants  from  Parents  crossed  with 
Pollen  from  other  Plants  of  the  same  Stock,  and  self-fertilised. 


•o 

o 

3s"s 

CG"3 

a 

I  "8 

ej 

=rl 

_C 

o  T£ 

.2 

3 

*s  a 

73   g 

"5  c 

CO 

j 

.s 

I! 

5  ™ 

3; 

si:J= 

. 

NAMES  OF  PLANTS. 

O    x 

'S    00 

?l 

•aS 

'53  "-* 

.c  o 

i  c 

73    |-1 

Jjl 

uS 

jj'O 

a»  *c 

c-  S 

Is; 

•="2 
S.S 

Us 

tt  % 

3 

> 

>  ?, 

&-r^ 

.2  - 

fr, 

«! 

fc 

<& 

<J° 

Ipomcea  purpurea — 1st  generation 

6 

86-00 

6 

65-66 

as  100  to 

76 

Ipomcea  purpurea — 2nd  generation 

6 

84-16 

6 

66-33 

jj 

j> 

79 

Ipomoea  purpurea — 3rd  generation 

6 

77-41 

6 

52-83 

>) 

jj 

68 

Ipomcea  purpurea — 4th  generation 

7 

69-78 

7 

60-14 

>) 

jj 

86 

Ipomoea  purpurea — 5th  generation 

6 

82-54 

6 

62-33 

» 

jj 

75 

Ipomoea  purpurea — 6th  generation 

6 

87-50 

6 

63-16 

jj 

jj 

72 

Ipomoea  purpurea — 7th  generation 

9 

83-94 

9 

68-25 

jj 

jj 

81 

Ipomoea  purpurea — 8th  generation 

8 

113-25 

8 

96-65 

JJ 

jj 

85 

Ipomoea  purpurea — 9th  generation 

14 

81-39 

14 

64-07 

JJ 

jj 

79 

Ipomcea  purpurea-lOth  generation 

5 

93-70 

5 

50-40 

JJ 

JJ 

54 

JJ  umber  and  average  height  of  all) 

the    plant;    of  the    ten    genera- 1 

73 

85-84 

73 

66-02 

JJ 

j) 

77 

Mimulus  lutcus — three  first  gene-l 

rations,  before  the  new  and  taller  \ 

10 

8-19 

10 

5-29 

jj 

jj 

65 

self-fertilised  variety  appeared    j 

16 

51-33 

8 

35-87 

J> 

)j 

70 

Calceolaria — (common    greenhouse"! 

1 

19-50 

1 

15-00 

» 

JJ 

77 

Linaria  vulgaris 

3 

7-08 

3 

5-75 

JJ 

jj 

81 

Verbascum  thapsus       .... 

6 

65-34 

6 

56  50 

3) 

jj 

86 

Vandellia  nummularifolia — crossed  1 

and  self-fertilised  plants,  raised  > 

20 

4-30 

20 

4-27 

JJ 

jj 

99 

from  perfect  flowers.      .      .      .j 

Vandellia  nummularifolia — crossed  i 

and  self-fertilised   plants,  raised  1 
from     perfect    flowers :    second  | 

24 

3-60 

24 

3-38 

JJ 

)J 

94 

trial,  plants  crowded       .      .      .J 

Vandellia  nummularifolia— crossed  J 

plants  raised  from  perfect  flowers, ) 
and    self-fertilised    plants  froml 

20 

4-30 

20 

4-06 

JJ 

» 

94 

cleistogeue  flowers     .            .      . ) 

8 

32-06 

8 

29-14 

JJ 

)J 

90 

6 

27-85 

6 

21-16 

JJ 

JJ 

76 

4 

20-00 

4 

17-12 

JJ 

JJ 

86 

Thunbergia  alata 

6 

60-00 

6 

65-00 

JJ 

JJ 

108 

9 

41-08 

9 

39-00 

JJ 

J) 

95 

iberis  umbel  lata — the  self-fertilised) 
plants  of  the  3rd  generation      .) 

7 

19-12 

7 

16-39 

JJ 

s> 

86 

Chap.  VII. 


SUMMARY   OF   MEASUREMENTS. 


241 


Table  A — continued. 


NAMES  OF  PLANTS. 


•a 

•o 

.J. 

C  g 

d    . 

o  2 

°1 

ii 

S3 

cc*9 

-a 

O     GO 

O   c3 

lS 

tig 

C3  P« 

£  .2 

C5    ^H 

z 

O 

53 

■xj"" 

.=  o 
tc  o 


^aparer  vagum 

Eschscholtzia  californica — English  "> 
stock,  1st  generation       .      .      .J 

Eschscholtzia  californica — English) 
stock,  2nd  generation      .      .      .) 

Eschscholtzia  californica  —  Bra- 1 
zilian  stock,  1st  generation  .      .  j 

Eschscholtzia  californica  —  Bra- "I 
zilian  stock,  2ml  generation.      .J 

Eschscholtzia  californica — average' 
height  and  number  of  all  the 
plants  of  Eschscholtzia   . 

Reseda  lutea — grown  in  pots    . 

Reseda  lutea — grown  in  open  ground 

Reseda  odorata  —  self  -  fertilisedl 
seeds  from  a  highly  self-fertile  v 
plant,  grown  in  pots.      .      .      .} 

Reseda  odorata  —  self- fertilisedl 
seeds  from  a  highly  self-fertile  > 
plant,  grown  in  open  ground     . ) 

Reseda  odorata  —  self  -  fertilised  1 
seeds  from  a  semi-self-sterile  > 
plant,  grown  in  pots.     ".      .      .) 

Reseda  odorata  —  self- fertilised 
seeds  from  a  semi-self-sterile 
plant,  grown  in  open  ground 

Viola  tricolor 

Adonis  aestivalis 

Delphinium  consolida    .... 

Viscaria  oculata 

Dianthus  caryophyllus  —  open 
ground,  about 

Dianthus  caryophyllus — 2nd  gen 
eration,  in  pots,  crowded 

Dianthus  caryophyllus — 3rd  gen- 
eration, in  pots 

Dianthus  caryophyllus — offspring 
from  plants  of  the  3rd  self-feri 
lised  generation  crossed  by  inter-! 
crossed  plants  of  3rd  generation, 
compared  with  plants  of  4th  self- 
fertilised  generation  . 


:} 


15 

21-91 

15 

19-54 | 

4 

29-68 

4 

25-56 

11 

32-47 

11 

32-81 

14 

44-64 

14 

45-12 

18 

43-38 

19 

50-30 

47 

40-03 

48 

42-72 

24 

17-17 

24 

14-61 

8 

28-09 

8 

23-14 

19 

27-48 

19 

22-55 

8 

25-76 

8 

27-09 

20 

29-98 

20 

27-71 

8 

25-92 

8 

23-54 

14 

5-58 

14 

2-37 

4 

14-25 

4 

14-31 

6 

14-95 

6 

12-50 

15 

34-50 

15 

33-55 

6? 

28? 

6? 

24? 

2 

16-75 

2 

9-75 

8 

28-39 

8 

28-21 

15 

28-00 

10 

26-55 

86 


101 


101 


116 


107 


»>       »     82 
m       ii     82 


105 


92 


90 

42 

100 

84 

97 

86 
58 
99 


»    95 


242 


SUMMARY  OF  MEASUREMENTS. 


Chap.  VII. 


Table  A — continued. 

NAMES  OF  PLANTS. 

■a 

o    . 

*-  T3 

OS 
u 

a* 

-  s 

■a 

6  3 

c  a 

i! 

SI 

a 
fl 

* 

O 
fcC 

CO  a) 

*"  ■/"© 

Sn2 

1-  o 

c 

3 

Is 

> 
< 

t-S 

£  .2 

•3 

c 

a. 
< 

■=5  8 

8j     g 

-1?  .'2  cs 

Dianthus    caryophyllus  —  number] 

and  average    height   of   »11   the> 

31 

27-37 

26 

25-18 

as  100  to    9 

plants  of  Diaathus     .      .      .      .  J 

4 

13-25 

4 

14-43 

JJ 

„  109 

Pelargonium  zonale        .... 

7 

22-35 

7 

16-62 

JJ 

„     74 

8 

58-43 

8 

46-00 

JJ 

„     79 

Limnanthes  douglasii    .... 

16 

17-46 

16 

13-85 

JJ 

„     79 

Lupinus  luteus — 2nd  generation    . 

8 

30-78 

8 

25-21 

}> 

„     82 

Lupinus  pilosus  —  plants    of    two") 

2 

35-50 

3 

30-50 

5) 

„     86 

Phaseolus  multiflorus    .... 

5 

86-00 

5 

82-35 

yj 

„     96 

4 

34-62 

4 

39-68 

9} 

„  115 

Sarothamnus     scoparius  —  small'! 

6 

2-91 

6 

1-33 

j> 

„    46 

Sarothamuus  scoparius — the  three] 

survivors  on  each  side  after  three  > 

18-91 

11-83 

J? 

„     63 

Ononis  miuutissima       .... 

2 

19-81 

2 

17-37 

jj 

„     88 

4 

33-50 

4 

27-62 

jj 

„     82 

8 

24-62 

8 

26-31 

jj 

„  107 

2 

49-00 

2 

51-00 

5J 

„  104 

!{ 

rot 
measured. 

W 

not 
mea-ured. 

}» 

„  100 

Scabiosa  atro-purpurea. 

4 

17-12 

4 

15-37 

JJ 

„     90 

Lactuca  sativa — plants  of  two  gen-"l 

7 

19-43 

6 

16-00 

JJ 

„     82 

Specularia  speculum     .... 

4 

19-28 

4 

18-93 

JJ 

»     93 

Lobelia  ranmsa — 1st  generation 

4 

22-25 

4 

18-37 

JJ 

.,     82 

Lobelia  ramosa — 2nd  generation    . 

3 

23-33 

3 

19-00 

JJ 

„     81 

Lobelia  fulgens — 1st  generation     . 

2 

34-75 

2 

44-25 

JJ 

„  127 

Lobelia  fulgens — 2nd  generation    . 

23 

29-82 

23 

27-10 

JJ 

„     91 

Nemophila  insignis — half-grown    . 

Y2 

11-10 

12 

5-45 

JJ 

„     4f 

Netnophila  insignis — the  same  fully\ 

4 

33-28 

20-68 

4 

19-90 
21-18 

JJ 

„     60 
„  102 

5 

12-75 

5 

13-40 

JJ 

»  10-5 

Petunia  violacea — 1st  generation  . 

5 

30-80 

5 

26-00 

JJ 

„     84 

Petunia  violacea — 2nd  generation  . 

4 

40-50 

6 

26-25 

JJ 

„     65 

Petunia  violacea — 3rd  generation  . 

8 

40 -9o 

8 

53-87 

7J 

»  181 

Petunia  violacea — 4th  generation  . 

15 

46-79 

14 

32-39 

>J 

„     69 

Chap.  VII. 


SUMMARY   OP   MEASUREMENTS. 


243 


Table  A — continued. 


•a 

•3 

.Jh 

ik  <= 

•  j 

U 

1 

o 

<2i  55 

w-i 

3 

H 

6  s 

ii  3 

a 

c  - 

a 

£   C3 

J3  += 

•°  ~k 

■°  w 

^cc  3 

.5P-£ 

NAMES  OF  PLANTS. 

.3  ts 

o  & 

is 

73 

■&  c 

it 

u  5 

ffi.il 

i-S 

®    & 

o-oPh  S 

f  = 

U 

£  <c 

sc.2 

bo  g 
£  1 

13  fl 

3 

> 

3  — 

^ 

«  *« 

ft 

•4 

B 

<!"" 

Petunia  violacea — 4th    generation, "I 
from  a  distinct  parent     .      .      .  j 

13 

44-74 

13 

26-87 

as  100  to   60 

Petunia  violacea — 5th  generation  . 

22 

54-11 

21 

33-23 

„    61 

Petunia  violacea — 5th    generation,'! 

10 

38-27 

10 

23-31 

„     61 

in  open  ground / 

Petunia    violacea  —  Number    andl 

average  height  of  all  the  plants  > 

67 

46-53 

67 

33-12 

„     71 

in  pots  of  Petunia     .      .            .J 

Nicotiana  tabacum  —  1st  generation 

4 

18-50 

4 

32-75 

„  178 

Nicotiana  tabacum — 2nd  generation 

9 

53-84 

7 

51-78 

»     96 

Nicotiana  tabacum — 3rd  generation 

7 

95-25 

7 

79-60 

„     83 

Nicotians  tabacum — 3rd  generation"! 

but  raised  from  a  distinct  plant  J 

7 

70-78 

9 

71-30 

„  101 

Nicotiana    tabacum — number    and  1 

average  height  of  all  the  plants) 

27 

63-73 

27 

61-31 

„     96 

Cyclamen  persicum 

8 

9-49 

8? 

7-50 

„     79 

6 

42-20 

6 

33-35 

„     69 

Primula    sinensis  —  a     dimorphic"! 

8 

9-01 

8 

9-03 

„  100 

Fago|>yrutn  esculentum — a  dimor-1 

15 

38-06 

15 

26-13 

„     69 

Beta  vulgaris— in  pots. 

8 

34-09 

8 

29-81 

„     87 

Beta  vulgaris — in  open  ground 

8 

30-92 

8 

30-70 

„     99 

Canna  warscewiczi — plants  of  three"! 

34 

35-98 

34 

36-39 

„  101 

Zea  mays — in   pots,  whilst  young,) 
measured  to  tips  of  leaves    .      .j 

15 

20-19 

15 

17-57 

.     87 

,,     (->i 

Zea  mays — when  full  grown,  after  1 

the  death  of  some,  measured  to  > 

68-10 

62-34 

„     91 

tips  of  leaves ) 

Zea  mays — when  full  grown,  afterl 

the  deaih  of  some,  measured  to> 

66-51 

61-59 

„     93 

Zea  mays — grown  in  open  ground,^ 
measured  to  tips  of  leaves     .      ./ 

10 

54-00 

10 

44-55 

„    83 

Zea  mays — grown  in  open  ground,  I 
measured  to  tips  of  flowers  .      .  J 

53-96 

43-45 

»     80 

Phalaris  canadensis—  in  pots    . 

11 

38-90 

11 

35-69 

„     92 

Phalaris  canadensis — in  open  ground 

12  , 

35-78 

12 

33-50 

„     93 

244 


SUMMAEY   OF   MEASUREMENTS. 


Chap.  Y1L 


Table  B. — Relative  Weights  of  Plants  from  Parents  crossed  with 
Pollen  from  distinct  Plants  of  the  same  Stock,  and  Self-fertilistd. 


NAMES  OF  PLANTS. 


Number  I  Number 

of  Crossed    of  Self- 

Plauts.   I  fertilised 

Plants. 


Ipomoea  purpurea — plants  of  the   10th  "4 

generation / 

Vandellia  nummularifolia — 1st  genera-'^ 

tion j 

Brassica  oleracea — 1st  generation    . 
Eschscholtzia  californica — plants  of  the\ 

2nd  generation J 

Reseda  lutea — 1st  generation,  grown  in"! 

pots / 

Reseda  lutea — 1st  generation,  grown  in^ 

open  ground / 

Reseda    odorata — 1st    generation,     de-1 

scended    from    a    highly    self-fertile) 

plant,  grown  in  pots ) 

Reseda    odorata — 1st     generation,    de-l 

scended  from  a  semi-self-sterile  plant,  > 

grown  in  pots ) 

Dianthus  caryophyllus— plants  of  the"! 

3rd  generation / 

Petunia    violacea — plants    of    the    5th \ 

generation,  in  pots / 

Petunia    violacea — pleats    of    the    5th 'J 

generation,  in  open  ground     .      .      ./ 


Weight  of  the 
Crossed  PLv  ts 
taken  us  100. 


41 

9 

19 

24 


19 


20 


22 
10 


41 

9 

19 

24 


19 

20 

8 
21 
10 


as  100  to  44 

»   j>  97 

»   »  37 
„   »  118 

»      »  21 

»   »  40 

»   »  67 

»   j>  99 

49 

»        n     22 

„   „  36 


Chap.  VII. 


SUMMAET   OF   MEASIJEEMENTS. 


245 


TABLE  C. —  'Relative  Heights,  Weights,  and  Fertility  of  Plants  from 
Parents  crossed  oy  a  fresh  Stock,  and  from  Parents  either  self' 
fertilised  or  intercrossed  with  Plants  of  the  same  Stock. 


NAMES  OF  PLANTS  AND  NATURE 
OF  THE  EXPERIMENTS. 


■A3 

•a 

•SB 

a 

B>£ 

£(3 

§ 

13 

S  3 

a  g 

.ss 

^c  § 

"S^ 

°~s 

S3 

t* 

£r- 

Kig 

<) 

•-  o 

1?: 


II: 


Ipomoea  purpurea  —  offspring  of 
plants  intercrossed  for  nine  gen- 
erations and  then  crossed  by  a 
fresh  stock,  compared  with 
plants  of  the  10th  intercrossed 
generation 


V  19 


Ipomoea  purpurea  —  offspring  of 
plants  intercrossed  for  nine  gen- 
erations and  then  crossed  by  a 
fresh  stock,  compared  with 
plants  of  the  10th  intercrossed 
generation,  in  fertility    ... 

Mimulusluteus — offspring  of  plants'! 
self-fertilised  for  eight  genera- 1 
tions  and  then  crossed  by  a  fresh } 
stock,  compared  with  plants  of  1 
the  9th  self-fertilised  generation) 

Mimulusluteus — offspring  of  plants' 
self-fertilised  for  eight  genera- 
tions and  then  crossed  by  a  fresh  I 
stock,  compared  with  plants  of  j 
the  9th  self- fertilised  generation,) 
in  fertility J 

jlimulusluteus — offspring  of  plants' 
self- fertilised  for  eight  genera- 
tions and  then  ciossed  by  a  fresh 
stock,  compared  with  the  off- 
spring of  a  plant  self- fertilised 
for  eight  generations,  and  then 
intercrossed  with  another  self- 
fertilised  plant  of  the  same  gen- 
eration       , 


84-03 


19 


28 


21-62 


19 


28 


21-62 


27 


65-78  as  100  to    78 


10-44 


12-20 


51 


52 


56 


246 


SUMMAEY   OF   MEASUREMENTS. 


Chap.  VIL 


Table  C — continued. 


NAMES  OF  PLANTS  AND  NATURE 
OF  THE  EXPERIMENTS. 

C3 

s 

-*>  Si 

!| 

Z 

•a 

! 

1 

a 

-u  to 
.c'3 

•sis 

K 

60 
C3 

> 
< 

8  § 
5  oM 

v  S  p 

JK 

! 

.s 
as 

II 

w 

> 

<1 

Height,  Weight,  and  Fertility 
of  the  Plants  trom  the  Cro*s 
wiih  a  Fresh  Stock  taken  as 
100. 

Mimtilusluteus — offspring  of  plants) 
self-fertilised    for  eight  genera- 
tions and  then  crossed  by  a  fresh 
stock,    compared    with    the   off- 
spring of  a  plant  self-fertilised 
for  eight  generations,  and  then 
intercrossed    with   another   self- 
fertilised  plant  of  the  same  gen- 
eration, in  fertility    .             . 

Brassica    oleracea  —  offspring     of 
plants  self-fertilised  for  two  gen- 
erations and  then  crossed  by  a 
fresh      stock,     compared     with 
phints  of  the  3rd  self- fertilised 
generation,  by  weight     . 

Iberis    umbellata — offspring    from' 
English      variety     crossed       by 
slightly    different   Algerine   va- 
riety,   compared    with    the  self- 
fertilised  offspring  of  the  English 

Iberis    umbellata — offspring    from' 
English     variety,     crossed      by 
slightly        different        Algerine 
variety,  compared  with  the  self- 
fertilised  offspring  of  the  English 
variety,  in  fertility   . 

Eschscholtziacalifornica — offspring) 
of  a  Brazilian  stock  crossect  by  1 
an  English  stock,  compared  'rith> 
plants  of  the  Bi-azilian  stock  of) 
the  2nd  self-fertilised  geneiationj 

Eschscholtziacalifornica — offspring' 

of  a  Brazilian   stock  crossed  by 

a  English  stock,  compared  withl 

plants  of  the  Brazilian  stock  off 

the  2nd  self-fertilised  generation, 

6 
30 

19 

17-34 
45-92 

6 

29 

19 

15-51 
50-30 

as  100  to     4 

»      »    22 

»      »    89 

»       »     «5 
»       „  109 

»      »  "8 

Chap.  VII. 


SUMMARY   OF   MEASUREMENTS. 


247 


Table  C — continued. 


NAMES  OF  PLANTS  AND  NATURE 
OF  THE  EXPERIMENTS. 


Eschscholtzia  californica — offspringl 
of  a  Brazilian  stock  crossed  by  I 
an  English  stock,  compared  with! 
plants  of  the  Brazilian  stock  of 
the  2nd  self-fertilised  generation 
in  fertility 


Eschscholtzia  californica — offspring'' 
of  a  Brazilian  stock  crossed  by 
an  English  stock,  compared  with 
plants  of  the  Brazilian  stock  of 
the  2nd  intercrossed  generation, 
in  height  ........ 


Eschscholtziacalifornica — offspring' 
of  a  Brazilian  stock  crossed  by 
an  English  stock,  compared  with, 
plants  of  the  Brazilian  stock  of 
the  2nd  intercrossed  generation, 
in  weight t 


Eschscholtzia  californica — offspring" 
of  a  Brazilian  stock  crossed  by 
an  English  stock,  compared  with 
plants  of  the  Brazilian  stock  of 
thp  2nd  intercrossed  generation, 
in  fertility 


Dianthus  caryophyllus — offspring^ 
of  plants  self-fertilised  for  three 
generations  aud  then  crossed  by 
a  fre.-,h  stock,  compared  with 
plants  of  the  4th  self-fertilised 
generation 


•e£ 


Dianthus  caryophyllus — offspring') 
of  plants  self-fertilised  for  three 
generations  and  then  crossed  by 
a  fresh  stock,  compared  with 
plants  of  the  4th  self-fertilised 
generation,  in  fertility    . 


19 


16 


45-92 


32-82 


X 


~3   O 


ti  - ; 

X  ° 


18 


10 


43-38 


26-55 


as  100  to   40 


94 


,,100 


45 


81 


33 


24.8 


SUMMARY   OF   MEASUREMENTS. 


Chap.  VIL 


Table  C — continued. 


NAMES  OF  PLANTS  AND  NATURE 
OF  THE  EXPERIMENTS. 


515 


1  - 

a 

'.   z 

p* 

-  -3 

JS 

.    ? 

C 

J  r 

4 

"  to 

i~ 

■a 

.H-> 

_  = 

= 

M 

to 

t=r 

> 

z- 

<! 

Dianthus  caryophyllus — offspring1 
of  plants  self-fertilised  for  three 
generations  ami  then  crossed  bv 
a  fresh  stock,  compared  with  the, 
offspring  of  plants  self-fertilised 
for  three  generations  and  then 
crossed  by  plants  of  the  3rd 
intercrossed  generation    . 

Dianthus  caryophyllus — offspring1 
of  plants  self-fertilised  for  three 
generations  and  then  crossed  by 
a  fresh  stock,  compared  with  the 
offspring  of  plants  self-fertilised 
for  three  generations  anil  then 
crossed  by  plants  of  the  3rd 
intercrossed  generation,  in  fer- 
tility   


16 


Pisum  sativum — offspring  from  a' 
cross  between  two  closely  allied 
varieties,  compared  with  the  self- 
fertilised  offspring  of  one  of  the 
varieties,  or  with  intercrossed 
plants  of  the  same  stock 

Lathyrus  odoratus — offspring  from) 
two  varieties,  differing  only  in 
colour  of  their  flowers,  compared 
with  the  self-fertilised  offspring 
of  one  of  the  varieties  :  in  1st 
generation 


J-*sthyrus  odoratus — offspring  from" 
two  varieties,  differing  only  in 
colour  of  their  flowers  compared 
with  the  self-fertilised  offspring 
of  one  of  the  varieties  in  2nd 
generation 


32-82 


15 


i9-2c 


62-91 


28-00 


63-75 


55-31 


as  100  to  85 


45 


80 


88 


Chap.  VII. 


SUMMARY   OF   MEASUREMENTS. 


249 


Table  C —continued. 


NAMES  OF  PLANTS  AND  NATURE    ^  : 
OF  THE  EXPERIMENTS. 


go 

S3 


J  g 

•o 

13 

_  <3 

Eft 

s 

o 

c 

C  " 

^  Sao 

rf='3 

-t 

55 

1 

1F» 

t-rt 
Hi 

fc- 

ii _ 

< 

t»><» 


Petunia  violacea  —  offspring  of 
plants  self-fertilised  for  four 
generations  and  then  crossed  by 
a  fresh  stock,  compared  with 
plants  of  the  5th  self-fertilised 
generation,  in  height 

Petunia  violacea  —  offspring  of) 
plants  self-fertilised  for  four  I 
generations  and  then  crossed  by! 
a  fresh  stock,  compared  withj 
plants  of  the  5th  self-fertilised 
generation,  in  weight      .      .      J 

Petunia  violacea  —  offspring  of) 
plants  self-fertilised  for  four 
generations  and  then  crossed  by 
a  fresh  stock,  compared  with 
plants  of  the  5th  self-fertilised 
generation,  grown  in  open  ground, 
in  height __ 

Petunia  violacea  —  offspring  of| 
plants  self-fertilised  for  four 
generations  and  then  crossed  by 
a  fresh  stock,  compared  with 
plants  of  the  5th  self-fertilised 
generation,  grown  in  open  ground, 
in  weight 

Petunia  violacea  —  offspring  of) 
plants  self-fertilised  for  four 
generations  and  then  crossed  by 
a  fvesh  stock,  compared  with 
plauts  of  the  5th  self-fertilised 
generation,  grown  in  open  ground, 
in  fertility 

Petunia  violacea  —  offspring  of) 
plants  self-fertilised  for  four 
generations  and  then  crossed  bv 
a  fresh  stock,  compared  with 
plants  of  the  5th  intercrossed 
generation,  in  height      . 


21     50-05 


10 


36-67 


21 


50-05 


21     33-23    as  100  to  66 


10 


22 


23-31 


54-11 


23 


63 


53 


46 


„  108 


250 


SUMMARY   OP   MEASUREMENTS. 


Chap.  VII. 


Table  C — continued. 


NAMES  OF  PLANTS  AND  NATLKE 
OF  THE  EXPERIMENTS. 


n 


Petunia  violacea  —  offspring  of 
plants  self- fertilised  for  four 
generations  and  then  crossed  by  I 
a  fresh  stock,  compared  with 
plants  of  the  5th  intercrossed 
generation,  in  weight 

Petunia  violacea  —  offspring  of| 
plants  self-fertilised  for  four 
generations  and  then  crossed  by 
a  fresh  stock,  compared  with 
plants  of  the  5th  intercrossed 
generation,  grown  in  open  ground, 
in  height 


Petunia  violacea  —  offspring  of) 
plants  self-fertilised  for  four 
generations  and  then  crossed  by 
a  fresh  stock,  compared  with 
plants  of  the  5th  intercrossed 
generation,  grown  in  open  ground, 
in  weight 


Petunia  violacea  —  offspring  of) 
plants  self-fertilised  for  four 
generations  and  then  crossed  by 
a  fresh  stock,  compared  with 
plants  of  the  5th  intercrossed 
generation,  grown  in  open  ground, 
in  fertility      .... 

Nicotiana  tabacum — offspring  of) 
plants  self-fertilised  for  three 
generations  and  then  crossed  by 
a  slightly  different  variety,  com- 
pared with  plants  of  the  4th 
self-fertilised  generation,  grown 
not  much  crowded  in  pots,  in 
height 


10 


26 


is  100  to  101 


36-67 


10 


38-27 


,,104 


146 


63-29 


26 


54 


41-67 


66 


Chap.  VII. 


SUMMAEY   OF   MEASUREMENTS. 


251 


Table  C— continued. 


NAMES  OF  PLANTS  AND  NATURE 
OF  THE  EXPERIMENTS. 


a* 

is 


^s 


■"  ■£  J3 


Nicotiana  tabacum — offspring  of) 
plants  self-fertilised  for  three 
generations  and  then  crossed  by 
a  slightly  different  variety,  com- 
pared with  plants  of  the  4th 
self-fertilised  generation,  grown 
much  crowded  in  pots,  in  heightj 

Nicotiana  tabacum — offspring  of 
plants  self-fertilised  for  three 
generations  and  then  crossed  by 
a  slightly  different  variety,  com- 
pared with  plants  of  the  4th 
self-fertilised  generation,  grown 
much  crowded  in  pots,  in  weight 

Nicotiana  tabacum — offspring  of 
plants  self-fertilised  for  three 
generations  and  then  crossed  by 
a  slightly  different  variety,  com- 
pared with  plants  of  the  4th 
self-fertilised  generation,  grown 
in  open  ground,  in  height     . 

Nicotiana  tabacum — offspring  of 
plants  self-fertilised  for  three 
generations  and  then  crossed  by 
a  slightly  different  variety,  com- 
pared with  plants  of  the  4th 
self-fertilised  generation,  grown 
in  open  ground,  in  weight    . 

Anagallis  collina — offspring  from  a) 
red  variety  crossed  by  a  blue 
variety,  compared  with  the  self- 
iertilised  offspring  of  the  red 
variety 


12 


20 


31-53 


48-74 


27-62 


12     17-21 


20    35-20 


as  100  to  54 


37 


72 


3     1821 


63 


66 


252 


SUMMARY   OF   MEASUREMENTS. 


Chap.  VII. 


Table  C — continued. 


NAMES  OF  PLANTS  AND  NATURE 
OF  THE  EXPERIMENTS. 

as 

is 

—  £ 

J,    =3 

*»  a 
ft 
•II 

16 
53 

■a 

0 
03 

a 

■5  3 

~-    -0 

s 

a> 
to 

C3 

> 

-A 

if 

Si- 

■a 

13 
a 

Qi 

.5 
.£  £* 

ST.® 

w 

to 

cS 
> 

¥J 

<v  %  s 
■c  _  24 

§?2 

*-"  u  03 

*  S  S3     . 

Anagallis  col  Una — offspring  from  a' 
red  variety  crossed    by    a   blue 
vaiiety,  compared  with  the  self- > 
fertilised    offspring    of    the    red 
variety,  in  fertility    . 

Primula  veris — offspring  from  long-') 
styled  plants  of  tho  3rd  illegiti- 
mate  generation,  crossed    by    al 
fresh      stock,     compared     with] 
plants   of  the   4th    illegitimate 
and  self-fertilised  generation 

Primula  veris — offspring  from  long-") 
styled  plants  of  the  ord  illegiti- 
mate   generation,  crossed    by    a 
fresh      stock,     compared      with^ 
plants    of  the    4th    illegitimate 
and  self-fertilised  generation,  in 

Primula  veris — offspring  from  long-1) 
styled  plants  of  the  3rd  illegiti- 
mate   generation,  crossed    by    a 
fresh     stock,     compared      with}' 
plants    of  the  4th    illegitimate 
and  self-fertilised  generation,  in 
fertility  in  following  year    . 

Primula  veris    (equal-styled,    red-1 
flowered  variety) — offspring  from  j 
plants    self-fertilised     for     t\vo| 
generations  and  then  crossed  by  aj- 
different  variety,  compared  with 
plants  of  the  3rd  self-fertilised 

Primula   veris    (equal-Jtyled,  red-1) 
flowered  variety) — offspring  from 
plants      self-fertilised    for     two 
generations  and  then  crossed  bva> 
different  variety,  compared  with 
plants  of  the  3rd  self-fertilised 
generation,  in  fertility    . 

8 

3 

1 

7*03 

8-66 

8 

3 

3-21 

7-33 

as  100  to    6 
»      »    46 

»          »          « 

Ohak  VII.  TABLE  C.  253 

In  these  three  tables  the-  measurements  of  fifty-seven 
species,  belonging  to  fifty  two  genera  and  to  thirty 
great  natural  families,  are  given.  The  species  are 
natives  of  various  parts  of  the  world.  The  number 
of  crossed  plants,  including  those  derived  from  a  cross 
between  plants  of  the  same  stock  and  of  two  different 
stocks,  amounts  to  1,101 ;  and  the  number  of  self-fer- 
tilised plants  (including  a  few  in  Table  C  derived 
from  a  cross  between  plants  of  the  same  old  stock) 
is  1,076.  Their  growth  was  observed  from  the  germi- 
nation of  the  seeds  to  maturity ;  and  most  of  them 
were  measured  twice  and  some  thrice.  The  various 
precautions  taken  to  prevent  either  lot  being  unduly 
favoured,  have  been  described  in  the  introductory 
chapter.  Bearing  all  these  circumstances  in  mind,  it 
may  be  admitted  that  we  have  a  fair  basis  for  judging 
of  the  comparative  effects  of  cross-fertilisation  and  of 
self-fertilisation  on  the  growth  of  the  offspring. 

It  will  be  the  most  convenient  plan  first  to  consider 
the  results  given  in  Table  C,  as  an  opportunity  will  thus 
be  afforded  of  incidentally  discussing  some  important 
points.  If  the  reader  will  look  down  the  right-hand 
column  of  this  table,  he  will  see  at  a  glance  what  an 
extraordinary  advantage  in  height,  weight,  and  fer- 
tility the  plants  derived  from  a  cross  with  a  fresh  stock 
or  with  another  sub- variety  have  over  the  self-fertilised 
plants,  as  well  as  over  the  intercrossed  plants  of  the 
same  old  stock.  There  are  only  two  exceptions  to  this 
rule,  and  these  are  hardly  real  ones.  In  the  case  of 
Eschscholtzia,  the  advantage  is  confined  to  fertility. 
In  that  of  Petunia,  though  the  plants  derived  from  a 
cross  with  a  fresh  stock  had  an  immense  superiority  in 
height,  weight,  and  fertility  over  the  self-fertilised 
plants,  they  were  conquered  by  the  intercrossed  plants 
of  the  same  old  stock  in  height  and  weight,  but  not 


254  SUMMAKT  OF  MEASUREMENTS  Chap.  VII. 

in  fertility.  It  has,  however,  been  shown  that  the 
superiority  of  these  intercrossed  plants  in  height  and 
weight  was  in  all  probability  not  real ;  for  if  the  two 
sets  had  been  allowed  to  grow  for  another  month,  it  is 
almost  certain  that  those  from  a  cross  with  the  fresh 
stock  would  have  been  victorious  in  every  way  over 
the  intercrossed  plants. 

Before  we  consider  in  detail  the  several  cases  given 
in  Table  C,  some  preliminary  remarks  must  be  made. 
There  is  the  clearest  evidence,  as  we  shall  presently 
see,  that  the  advantage  of  a  cross  depends  wholly  on 
the  plants  differing  somewhat  in  constitution  ;  and  that 
the  disadvantages  of  self-fertilisation  depend  on  the  two 
parents,  which  are  combined  in  the  same  hermaphrodite 
flower,  having  a  closely  similar  constitution.  A  certain 
amount  of  differentiation  in  the  sexual  elements  seems 
indispensable  for  the  full  fertility  of  the  parents,  and 
for  the  full  vigour  of  the  offspring.  All  the  individuals 
of  the  same  species,  even  those  produced  in  a  state  of 
nature,  differ  somewhat,  though  often  very  slightly, 
from  one  another  in  external  characters  and  probably  in 
constitution.  This  obviously  holds  good  between  the 
varieties  of  the  same  species,  as  far  as  external  characters 
are  concerned ;  and  much  evidence  could  be  advanced 
with  respect  to  their  generally  differing  somewhat  m 
constitution.  There  can  hardly  be  a  doubt  that  the 
differences  of  all  kinds  between  the  individuals  and 
varieties  of  the  same  species  depend  largely,  and  as  I 
believe  exclusively,  on  their  progenitors  having  been 
subjected  to  different  conditions  ;  though  the  conditions 
to  which  the  individuals  of  the  same  species  are  ex- 
posed in  a  state  of  nature  often  falsely  appear  to  us  the 
same.  For  instance,  the  individuals  growing  together 
are  necessarily  exposed  to  the  same  climate,  and  they 
seem  to  us  at  first  sight  to  be  subjected  to  identically 


Chap.  VH.  TABLE  0.  255 

the  same  conditions  ;  but  this  can  hardly  be  the  case, 
except  under  the  unusual  contingency  of  each  individual 
being  surrounded  by  other  kinds  of  plants  in  exactly 
the  same  proportional  numbers.  For  the  surround- 
ing plants  absorb  different  amounts  of  various  sub- 
stances from  the  soil,  and  thus  greatly  affect  the 
nourishment  and  even  the  life  of  the  individuals  of 
any  particular  species.  These  will  also  be  shaded  and 
otherwise  affected  by  the  nature  of  the  surrounding 
plants.  Moreover,  seeds  often  lie  dormant  in  the 
ground,  and  those  which  germinate  during  any  one 
year  will  often  have  been  matured  during  very  different 
seasons.  Seeds  are  widely  dispersed  by  various  means, 
and  some  will  occasionally  be  brought  from  distant 
stations,  where  their  parents  have  grown  under  some- 
what different  conditions,  and  the  plants  produced 
from  such  seeds  will  intercross  with  the  old  residents, 
thus  mingling  their  constitutional  peculiarities  in  all 
sorts  of  proportions. 

Plants  when  first  subjected  to  culture,  even  in  their 
native  country,  cannot  fail  to  be  exposed  to  greatly 
changed  conditions  of  life,  more  especially  from 
growing  in  cleared  ground,  and  from  not  having  to 
compete  with  many  or  any  surrounding  plants.  They 
are  thus  enabled  to  absorb  whatever  they  require 
which  the  soil  may  contain.  Fresh  seeds  are  often 
brought  from  distant  gardens,  where  the  parent- 
plants  have  been  subjected  to  different  conditions. 
Cultivated  plants  like  those  in  a  state  of  nature 
frequently  intercross,  and  will  thus  mingle  their 
3onstitutional  peculiarities.  On  the  other  hand,  as 
long  as  the  individuals  of  any  species  are  culti- 
vated in  the  same  garden,  they  will  apparently  be 
subjected  to  more  uniform  conditions  than  plants  in  a 
state  of  nature,  as  the  individuals  have  not  to  compete 
12 


256  SUMMAKY   OF  MEASUREMENTS.         Chap.  VII 

with  various  surrounding  species.  The  seeds  sown  at 
the  same  time  in  a  garden  have  generally  been  matured 
during  the  same  season  and  in  the  same  place ;  and  in 
this  respect  they  differ  much  from  the  seeds  sown  by 
the  hand  of  nature.  Some  exotic  plants  are  not 
frequented  by  the  native  insects  in  their  new  home, 
and  therefore  are  not  intercrossed ;  and  this  appears 
to  be  a  highly  important  factor  in  the  individuals 
acquiring  uniformity  of  constitution. 

In  my  experiments  the  greatest  care  was  taken  that 
in  each  generation  all  the  crossed  and  self-fertilised 
plants  should  be  subjected  to  the  same  conditions. 
Not  that  the  conditions  were  absolutely  the  same,  for 
the  more  vigorous  individuals  will  have  robbed  the 
weaker  ones  of  nutriment,  and  likewise  of  water  when 
the  soil  in  the  pots  was  becoming  dry ;  and  both  lots 
at  one  end  of  the  pot  will  have  received  a  little  more 
light  than  those  at  the  other  end.  In  the  successive 
generations,  the  plants  were  subjected  to  somewhat 
different  conditions,  for  the  seasons  necessarily  varied, 
and  they  were  sometimes  raised  at  different  periods  of 
the  year.  But  as  they  were  all  kept  under  glass,  they 
were  exposed  to  far  less  abrupt  and  great  changes  of 
temperature  and  moisture  than  are  plants  growing  out 
of  doors.  With  respect  to  the  intercrossed  plants,  their 
first  parents,  which  were  not  related,  would  almost 
certainly  have  differed  somewhat  in  constitution  ;  and 
such  constitutional  peculiarities  would  be  variously 
mingled  in  each  succeeding  intercrossed  generation, 
being  sometimes  augmented,  but  more  commonly 
neutralised  in  a  greater  or  less  degree,  and  sometimes 
revived  through  reversion ;  just  as  we  know  to  be  the 
case  with  the  external  characters  of  crossed  species  and 
varieties.  With  the  plants  which  were  self-fertilised 
during  the  successive  generations,  this  latter  important 


Chap.  VII  TABLE   C.  257 

source  of  some  diversity  of  constitution  will  have  been 
wholly  eliminated ;  and  the  sexual  elements  produced 
by  the  same  flower  must  have  been  developed  under  as 
nearly  the  same  conditions  as  it  is  possible  to  conceive. 

In  Table  C  the  crossed  plants  are  the  offspring  of  a 
cross  with  a  fresh  stock,  or  with  a  distinct  variety ;  and 
they  were  put  into  competition  either  with  self-fertilised 
plants,  or  with  intercrossed  plants  of  the  same  old  stock. 
By  the  term  fresh  stock  I  mean  a  non-related  plant, 
the  progenitors  of  which  have  been  raised  during  some 
generations  in  another  garden,  and  have  consequently 
been  exposed  to  somewhat  different  conditions.  In  the 
case  of  Nicotiana,  Iberis,  the  red  variety  of  Primula,  the 
common  Pea,  and  perhaps  Anagallis,  the  plants  which 
were  crossed  may  be  ranked  as  distinct  varieties  or 
sub-varieties  of  the  same  species ;  but  with  Ipomoea, 
Mimulus,  Dianthus,  and  Petunia,  the  plants  which 
were  crossed  differed  exclusively  in  the  tint  of  their 
flowers ;  and  as  a  large  proportion  of  the  plants  raised 
from  the  same  lot  of  purchased  seeds  thus  varied,  the 
differences  may  be  estimated  as  merely  individual. 
Having  made  these  preliminary  remarks,  we  will  now 
consider  in  detail  the  several  cases  given  in  Table  C, 
and  they  are  well  worthy  of  full  consideration. 

(1.)  Ipomoea  purpurea. — Plants  growing  in  the  same 
pots,  and  subjected  in  each  generation  to  the  same 
conditions,  were  intercrossed  for  nine  consecutive 
generations.  These  intercrossed  plants  thus  became  in 
the  later  generations  more  or  less  closely  inter-related. 
Flowers  on  the  plants  of  the  ninth  intercrossed  genera- 
tion were  fertilised  with  pollen  taken  from  a  fresh 
stock,  and  seedlings  thus  raised.  Other  flowers  on  the 
same  intercrossed  plants  were  fertilised  with  pollen 
from  another  intercrossed  plant,  producing  seedlings  of 
the  tenth  intercrossed  generation.     These  two  sets  of 


258  SUMMARY   OF   MEASUREMENTS.  Chap.  VII. 

seedlings  were  grown  in  competition  with  one  another, 
and  differed  greatly  in  height  and  fertility.  For  the 
offspring  from  the  cross  with  a  fresh  stock  exceeded  in 
height  the  intercrossed  plants  in  the  ratio  of  100  to  78  ; 
and  this  is  nearly  the  same  excess  which  the  inter- 
crossed had  over  the  self-fertilised  plants  in  all  ten 
generations  taken  together,  namely,  as  100  to  77.  The 
plants  raised  from  the  cross  with  a  fresh  stock  were 
also  greatly  superior  in  fertility  to  the  intercrossed, 
namely,  in  the  ratio  of  100  to  51,  as  judged  by  the 
relative  weight  of  the  seed-capsules  produced  by  an 
equal  number  of  plants  of  the  two  sets,  both  having 
been  left  to  be  naturally  fertilised.  It  should  be 
especially  observed  that  none  of  the  plants  of  either  lot 
were  the  product  of  self-fertilisation.  On  the  contrary, 
the  intercrossed  plants  had  certainly  been  crossed  for  the 
last  ten  generations,  and  probably,  during  all  previous 
generations,  as  we  may  infer  from  the  structure  of  the 
flowers  and  from  the  frequency  of  the  visits  of  humble- 
bees.  And  so  it  will  have  been  with  the  parent-plants 
of  the  fresh  stock.  The  whole  great  difference  in  height 
and  fertility  between  the  two  lots  must  be  attributed  to 
the  one  being  the  product  of  a  cross  with  pollen  from  a 
fresh  stock,  and  the  other  of  a  cross  between  plants  of 
the  same  old  stock. 

This  species  offers  another  interesting  case.  In  the 
five  first  generations  in  which  intercrossed  and  self- 
fertilised  plants  were  put  into  competition  with  one 
another,  every  single  intercrossed  plant  beat  its  self- 
fertilised  antagonist,  except  in  one  instance,  in  which 
they  were  equal  in  height.  But  in  the  sixth  gene- 
ration a  plant  appeared,  named  by  me  the  Hero,  re- 
markable for  its  tallness  and  increased  self-fertility, 
and  which  transmitted  its  characters  to  the  next  three 
generations.     The  children  of  Hero  were  again  self- 


Chap.  VII.  TABLE   C.  259 

fertilised,  forming  the  eighth  self-fertilised  generation, 
and  were  likewise  intercrossed  one  with  another ;  but 
this  cross  between  plants  which  had  been  subjected 
to  the  same  conditions  and  had  been  self-fertilised 
during  the  seven  previous  generations,  did  not  effect 
the  least  good ;  for  the  intercrossed  grandchildren  were 
actually  shorter  than  the  self-fertilised  grandchildren, 
in  the  ratio  of  100  to  107.  We  here  see  that  the 
mere  act  of  crossing  two  distinct  plants  does  not  by 
itself  benefit  the  offspring.  This  case  is  almost  the 
converse  of  that  in  the  last  paragraph,  in  which  the 
offspring  profited  so  greatly  by  a  cross  with  a  fresh 
stock.  A  similar  trial  was  made  with  the  descendants 
of  Hero  in  the  following  generation,  and  with  the  same 
result.  But  the  trial  cannot  be  fully  trusted,  owing 
to  the  extremely  unhealthy  condition  of  the  plants. 
Subject  to  this  same  serious  cause  of  doubt,  even  a 
cross  with  a  fresh  stock  did  not  benefit  the  great- 
grandchildren of  Hero ;  and  if  this  were  really  the  case, 
it  is  the  greatest  anomaly  observed  by  me  in  all  my 
experiments. 

(2.)  Mimulus  luteus. — During  the  three  first  genera- 
tions the  intercrossed  plants  taken  together  exceeded 
in  height  the  self-fertilised  taken  together,  in  the  ratio 
of  100  to  65,  and  in  fertility  in  a  still  higher  degree. 
In  the  fourth  generation  a  new  variety,  which  grew 
taller  and  had  whiter  and  larger  flowers  than  the  old 
varieties,  began  to  prevail,  especially  amongst  the  self- 
fertilised  plants.  This  variety  transmitted  its  characters 
with  remarkable  fidelity,  so  that  all  the  plants  in  the 
later  self-fertilised  generations  belonged  to  it.  These 
consequently  exceeded  the  intercrossed  plants  consider- 
ably in  height.  Thus  in  the  seventh  generation  the 
intercrossed  plants  were  to  the  self-fertilised  in  height 
as  100  to  137.     It  is  a  more  remarkable  fact  that  the 


260  SUMMARY  OE  MEASUREMENTS.         Chap.  VII. 

self-fertilised  plants  of  the  sixth  generation  had  become 
much  more  fertile  than  the  intercrossed  plants,  judging 
by  the  number  of  capsules  spontaneously  produced,  in 
the  ratio  of  147  to  100.  This  variety,  which  as  we 
have  seen  appeared  amongst  the  plants  of  the  fourth 
self-fertilised  generation,  resembles  in  almost  all  its 
constitutional  peculiarities  the  variety  called  Hero 
which  appeared  in  the  sixth  self-fertilised  generation 
of  Ipoinoea.  No  other  such  case,  with  the  partial  ex- 
ception of  that  of  Nicotiana,  occurred  in  my  experi- 
ments, carried  on  during  eleven  years. 

Two  plants  of  this  variety  of  Mimulus,  belonging  to 
the  sixth  self-fertilised  generation,  and  growing  in 
separate  pots,  were  intercrossed ;  and  some  flowers  on 
the  same  plants  were  again  self-fertilised.  From  the 
seeds  thus  obtained,  plants  derived  from  a  cross 
between  the  self-fertilised  plants,  and  others  of  the 
seventh  self-fertilised  generation,  were  raised.  But. 
this  cross  did  not  do  the  least  good,  the  intercrossed 
plants  being  inferior  in  height  to  the  self-fertilised,  in 
the  ratio  of  100  to  110.  This  case  is  exactly  parallel 
with  that  given  under  Ipomoea,  of  the  grandchildren 
of  Hero,  and  apparently  of  its  great-grandchildren ; 
for  the  seedlings  raised  by  intercrossing  these  plants 
were  not  in  any  way  superior  to  those  of  the  cor- 
responding generation  raised  from  the  self-fertilised 
flowers.  Therefore  in  these  several  cases  the  crossing 
of  plants,  which  had  been  self-fertilised  for  several 
generations  and  which  had  been  cultivated  all  the 
time  under  as  nearly  as  possible  the  same  conditions, 
was  not  in  the  least  beneficial. 

Another  experiment  was  now  tried.  Firstly,  plants 
of  the  eighth  self-fertilised  generation  were  again 
self- fertilised,  producing  plants  of  the  ninth  self- 
fertiJised  generation.    Secondly,  two  of  the  plants  of  the 


Chap.  VII.  TABLE  C.  261 

eighth  self-fertilised  generation  were  intercrossed  one 
with  another,  as  in  the  experiment  above  referred  to ; 
but  this  was  now  effected  on  plants  which  had  been 
subjected   to   two   additional   generations  of   self -fer- 
tilisation.    Thirdly,  the  same  plants  of  the  eighth  self- 
fertilised   generation  were   crossed  with   pollen   from 
plants  of  a  fresh  stock  brought  from  a  distant  garden. 
Numerous  plants  were  raised  from  these  three  sets  of 
seeds,  and  grown  in   competition  with   one  another. 
The  plants  derived  from  a  cross  between  the  self-fer- 
tilised plants  exceeded  in  height  by  a  little  the  self- 
fertilised,  viz.,  as  100  to  92 ;  and  in  fertility  in  a  greater 
degree,  viz.,  as  100  to  73.     I  do  not  know  whether 
this  difference  in  the  result,  compared  with  that  in  the 
previous  case,  can  be  accounted  for  by  the  increased 
deterioration   of  the  self-fertilised   plants    from    two 
additional   generations    of  self-fertilisation,   and    the 
consequent  advantage  of  any  cross  whatever,  although 
merely  between  the  self-fertilised  plants.    But  however 
this  may  be,  the  effects  of  crossing  the  self-fertilised 
plants  of  the  eighth  generation  with  a  fresh  stock  were 
extremely  striking  ;  for  the  seedlings  thus  raised  were 
to  the  self-fertilised  of  the  ninth  generation  as  100  to 
52  in  height,  and  as  100  to  3  in  fertility  !     They  were 
also  to  the  intercrossed  plants  (derived  from  crossing 
two  of  the  self-fertilised  plants  of  the  eighth  generation) 
in  height  as  100  to  56,  and  in  fertility  as  100  to  4. 
Better  evidence  could  hardly  be  desired  of  the  potent 
influence  of  a  cross  with  a  fresh  stock  on  plants  which 
had  been  self-fertilised  for  eight  generations,  and  had 
been   cultivated   all   the   time  under  nearly  uniform 
conditions,  in   comparison   with   plants   self-fertilised 
for  nine  generations  continuously,  or  then  once  inter- 
crossed, namely  in  the  last  generation. 

(3.)    Brassica  oleracea. — Some   flowers  on   cabbage 


262  SUMMAKY   OF   MEASUREMENTS.         Chap.  VII. 

plants  of  the  second  self-fertilised  generation  were 
crossed  with  pollen  from  a  plant  of  the  same  variety 
brought  from  a  distant  garden,  and  other  flowers  were 
again  self-fertilised.  Plants  derived  from  a  cross  with 
a  fresh  stock  and  plants  of  the  third  self-fertilised 
generation  were  thus  raised.  The  former  were  to 
the  self-fertilised  in  weight  as  100  to  22;  and  this 
enormous  difference  must  be  attributed  in  part  to 
the  beneficial  effects  of  a  cross  with  a  fresh  stock, 
and  in  part  to  the  deteriorating  effects  of  self-fertilisa- 
tion continued  during  three  generations. 

(4.)  Iberis  umbellata.  —  Seedlings  from  a  crimson 
English  variety  crossed  by  a  pale-coloured  variety 
which  had  been  grown  for  some  generations  in  Algiers, 
were  to  the  self-fertilised  seedlings  from  the  crimson 
variety  in  height  as  100  to  89,  and  as  100  to  75  in 
fertility.  I  am  surprised  that  this  cross  with  another 
variety  did  not  produce  a  still  more  strongly  marked 
beneficial  effect ;  for  some  intercrossed  plants  of  the 
crimson  English  variety,  put  into  competition  with 
plants  of  the  same  variety  self-fertilised  during  three 
generations,  were  in  height  as  100  to  86,  and  in 
fertility  as  100  to  75.  The  slightly  greater  difference 
in  height  in  this  latter  case,  may  possibly  be  attributed 
to  the  deteriorating  effects  of  self-fertilisation  carried 
on  for  two  additional  generations. 

(5.)  Eschscholtzia  californica. — This  plant  offers  an 
almost  unique  case,  inasmuch  as  the  good  effects  of 
a  cross  are  confined  to  the  reproductive  system. 
Intercrossed  and  self-fertilised  plants  of  the  English 
stock  did  not  differ  in  height  (nor  in  weight,  as  far  as 
was  ascertained,)  in  any  constant  manner ;  the  self- 
fertilised  plants  usually  having  the  advantage.  So  it 
was  with  the  offspring  of  plants  of  the  Brazilian  stock, 
tried  in  the  same  manner.   The  parent-plants,  however, 


Chap.  VII.  TABLE   C.  263 

of  the  English  stock  produced  many  more  seeds  when 
fertilised  with  pollen  from  another  plant  than  when 
self-fertilised;  and  in  Brazil  the  parent-plants  were 
absolutely  sterile  unless  they  were  fertilised  with 
pollen  from  another  plant.  Intercrossed  seedlings, 
raised  in  England  from  the  Brazilian  stock,  compared 
with  self-fertilised  seedlings  of  the  corresponding  second 
generation,  yielded  seeds  in  number  as  100  to  89  ;  both 
lots  of  plants  being  left  freely  exposed  to  the  visits  of 
insects.  If  we  now  turn  to  the  effects  of  crossing 
plants  of  the  Brazilian  stock  with  pollen  from  the 
English  stock, — so  that  plants  which  had  been  long 
exposed  to  very  different  conditions  were  intercrossed, 
— we  find  that  the  offspring  were,  as  before,  inferior  in 
height  and  weight  to  the  plants  of  the  Brazilian  stock 
after  two  generations  of  self-fertilisation,  but  were 
superior  to  them  in  the  most  marked  manner  in  the 
number  of  seeds  produced,  namely,  as  100  to  40  ;  both 
lots  of  plants  being  left  freely  exposed  to  the  visits  of 
insects. 

In  the  case  of  Ipomoea,  we  have  seen  that  the 
plants  derived  from  a  cross  with  a  fresh  stock  were 
superior  in  height  as  100  to  78,  and  in  fertility  as  100 
to  51,  to  the  plants  of  the  old  stock,  although  these 
had  been  intercrossed  during  the  last  ten  generations. 
With  Eschscholtzia  we  have  a  nearly  parallel  case, 
but  only  as  far  as  fertility  is  concerned,  for  the  plants 
derived  from  a  cross  with  a  fresh  stock  were  superior 
in  fertility  in  the  ratio  of  100  to  45  to  the  Brazilian 
plants,  which  had  been  artificially  intercrossed  in 
England  for  the  two  last  generations,  and  which  must 
have  been  naturally  intercrossed  by  insects  during  all 
previous  generations  in  Brazil,  where  otherwise  they 
are  quite  sterile. 

(6.)    Dianthus    caryopliyllus. — Plants    self-fertilised 


264  SUMMAKY  OF  MEASUREMENTS.         Chap.  VII. 

for  three  generations  were  crossed  with  pollen  from  a 
fresh  stock,  and  their  offspring  were  grown  in  compe- 
tition with  plants  of  the  fourth  self-fertilised  genera- 
tion. The  crossed  plants  thus  obtained  were  to  the 
self-fertilised  in  height  as  100  to  81,  and  in  fertility 
(both  lots  being  left  to  be  naturally  fertilised  by- 
insects)  as  100  to  33. 

These  same  crossed  plants  were  also  to  the  off- 
spring from  the  plants  of  the  third  self-fertilised  gene- 
ration crossed  by  the  intercrossed  plants  of  the  cor- 
responding generation,  in  height  as  100  to  85,  and  in 
fertility  as  100  to  45. 

We  thus  see  what  a  great  advantage  the  offspring 
from  a  cross  with  a  fresh  stock  had,  not  only  over  the 
self-fertilised  plants  of  the  fourth  generation,  but 
over  the  offspring  from  the  self-fertilised  plants  of  the 
third  generation,  when  crossed  by  the  intercrossed 
plants  of  the  old  stock. 

(7.)  Pisum  sativum. — It  has  been  shown  under  the 
head  of  this  species,  that  the  several  varieties  in  this 
country  almost  invariably  fertilise  themselves,  owing 
to  insects  rarely  visiting  the  flowers;  and  as  the 
plants  have  been  long  cultivated  under  nearly  similar 
conditions,  we  can  understand  why  a  cross  between 
two  individuals  of  the  same  variety  does  not  do  the 
least  good  to  the  offspring  either  in  height  or  fertility. 
This  case  is  almost  exactly  parallel  with  that  of 
Mimulus,  or  that  of  the  Ipomcea  named  Hero ;  for 
in  these  two  instances,  crossing  plants  which  had  been 
self-fertilised  for  seven  generations  did  not  at  all 
benefit  the  offspring.  On  the  other  hand,  a  cross 
between  two  varieties  of  the  pea  causes  a  marked 
superiority  in  the  growth  and  vigour  of  the  offspring, 
over  the  self-fertilised  plants  of  the  same  varieties, 
as  shown  by. two  excellent  observers.     From  my  own 


Chap.  VII.  TABLE  C.  265 

observations  (not  made  with  great  care)  the  offspring 
from  crossed  varieties  were  to  self-fertilised  plants  in 
height,  in  one  case  as  100  to  about  75,  and  in  a  second 
case  as  100  to  60. 

(8.)  Lathyrus  odoratus. — The  sweet-pea  is  in  the 
same  state  in  regard  to  self-fertilisation  as  the  common 
pea;  and  we  have  seen  that  seedlings  from  a  cross 
between  two  varieties,  which  differed  in  no  respect  ex- 
cept in  the  colour  of  their  flowers,  were  to  the  self-ferti- 
lised seedlings  from  the  same  mother-plant  in  height  as 
100  to  80 ;  and  in  the  second  generation  as  100  to  88. 
Unfortunately  I  did  not  ascertain  whether  crossing 
two  plants  of  the  same  variety  failed  to  produce  any 
beneficial  effect,  but  I  venture  to  predict  such  would 
be  the  result. 

(9.)  Petunia  violacea. — The  intercrossed  plants  of 
the  same  stock  in  four  out  of  the  five  successive  gene- 
rations plainly  exceeded  in  height  the  self-fertilised 
plants.  The  latter  in  the  fourth  generation  were 
crossed  by  a  fresh  stock,  and  the  seedlings  thus  obtained 
were  put  into  competition  with  the  self-fertilised  plants 
of  the  fifth  generation.  The  crossed  plants  exceeded 
the  self-fertilised  in  height  in  the  ratio  of  100  to  66, 
and  in  weight  as  100  to  23 ;  but  this  difference, 
though  so  great,  is  not  much  greater  than  that  between 
the  intercrossed  plants  of  the  same  stock  in  comparison 
with  the  self-fertilised  plants  of  the  corresponding- 
generation.  This  case,  therefore,  seems  at  first  sight 
opposed  to  the  rule  that  a  cross  with  a  fresh  stock  is 
much  more  beneficial  than  a  cross  between  individuals 
of  the  same  stock.  But  as  with  Eschscholtzia,  the 
reproductive  system  was  here  chiefly  benefited;  for 
the  plants  raised  from  the  cross  with  the  fresh  stock 
were  to  the  self-fertilised  plants  in  fertility,  both  lots 
being  naturally  fertilised,  as  100  to  46,  whereas  the 


266  SUMMAET  OF  MEASUEEMENTS.         Chap.  VIL 

intercrossed  plants  of  the  same  stock  were  to  the  self- 
fertilised  plants  of  the  corresponding  fifth  generation 
in  fertility  only  as  100  to  86. 

Although  at  the  time  of  measurement  the  plants 
raised  from  the  cross  with  the  fresh  stock  did  not 
exceed  in  height  or  weight  the  intercrossed  plants  of 
the  old  stock  (owing  to  the  growth  of  the  former  not 
having  been  completed,  as  explained  under  the  head 
of  this  species),  yet  they  exceeded  the  intercrossed 
plants  in  fertility  in  the  ratio  of  100  to  54.  This  fact 
is  interesting,  as  it  shows  that  plants  self-fertilised 
for  four  generations  and  then  crossed  by  a  fresh  stock, 
yielded  seedlings  which  were  nearly  twice  as  fertile  as 
those  from  plants  of  the  same  stock  which  had  been 
intercrossed  for  the  five  previous  generations.  We 
here  see,  as  with  Eschscholtzia  and  Dianthus,  that  the 
mere  act  of  crossing,  independently  of  the  state  of  the 
crossed  plants,  has  little  efficacy  in  giving  increased 
fertility  to  the  offspring.  The  same  conclusion  holds 
good,  as  we  have  already  seen,  in  the  analogous  cases  of 
Ipomoea,  Mimulus,  and  Dianthus,  with  respect  to  height. 

(10.)  Nicotiana  tdbacum.—Ky  plants  were  remark- 
ably self-fertile,  and  the  capsules  from  the  self-fertilised 
flowers  apparently  yielded  more  seeds  than  those  which 
were  cross-fertilised.  JSTo  insects  were  seen  to  visit  the 
flowers  in  the  hothouse,  and  I  suspect  that  the  stock 
on  which  I  experimented  had  been  raised  under  glass, 
and  had  been  self-fertilised  during  several  previous 
generations ;  if  so,  we  can  understand  why,  in  the  course 
of  three  generations,  the  crossed  seedlings  of  the  same 
stock  did  not  uniformly  exceed  in  height  the  self-ferti- 
lised seedlings.  But  the  case  is  complicated  by  indi- 
vidual plants  having  different  constitutions,  so  that  some 
of  the  crossed  and  self -fertilised  seedlings  raised  at  the 
same  time  from  the  same  parents  behaved  differently. 


Chap.  VII.  TABLE   C.  267 

However  this  may  be,  plants  raised  from  self-fertilised 
plants  of  the  third  generation  crossed  by  a  slightly 
different  sub-variety,  exceeded  greatly  in  height  and 
weight  the  self-fertilised  plants  of  the  fourth  genera- 
tion ;  and  the  trial  was  made  on  a  large  scale.  They 
exceeded  them  in  height  when  grown  in  pots,  and  not 
much  crowded,  in  the  ratio  of  100  to  66  ;  and  when 
much  crowded,  as  100  to  54.  These  crossed  plants,  when 
thus  subjected  to  severe  competition,  also  exceeded 
the  self-fertilised  in  weight  in  the  ratio  of  100  to  37. 
So  it  was,  but  in  a  less  degree  (as  may  be  seen  in 
Table  C),  when  the  two  lots  were  grown  out  of  doors 
and  not  subjected  to  any  mutual  competition.  Never- 
theless, strange  as  is  the  fact,  the  flowers  on  the 
mother-plants  of  the  third  self-fertilised  generation 
did  not  yield  more  seed  when  they  were  crossed  with 
pollen  from  plants  of  the  fresh  stock  than  when  they 
were  self-fertilised. 

(11.)  Anagallis  collina. — Plants  raised  from  a  red 
variety  crossed  by  another  plant  of  the  same  variety 
were  in  height  to  the  self-fertilised  plants  from  the 
red  variety  as  100  to  73.  When  the  flowers  on  the 
red  variety  were  fertilised  with  pollen  from  a  closely 
similar  blue-flowered  variety,  they  yielded  double  the 
number  of  seeds  to  what  they  did  when  crossed  by 
pollen  from  another  individual  of  the  same  red  variety, 
and  the  seeds  were  much  finer.  The  plants  raised 
from  this  cross  between  the  two  varieties  were  to  the 
self-fertilised  seedlings  from  the  red  variety,  in  height 
as  100  to  Q6,  and  in  fertility  as  100  to  6. 

(12.)  Primula  veris. — Some  flowers  on  long-styled 
plants  of  the  third  illegitimate  generation  were  legiti- 
mately crossed  with  pollen  from  a  fresh  stock,  and 
others  were  fertilised  with  their  own  pollen.  From 
the  seeds  thus    produced    crossed  plants,   and  self- 


268  SUMMAEY   OF  MEASUREMENTS.         Chap.  VII. 

fertilised  plants  of  the  fourth,  illegitimate  generation, 
were  raised.  The  former  were  to  the  latter  in 
height  as  100  to  46,  and  in  fertility  during  one 
year  as  100  to  5,  and  as  100  to  3  •  5  during  the  next 
year.  In  this  case,  however,  we  have  no  means  of 
distinguishing  between  the  evil  effects  of  illegitimate 
fertilisation  continued  during  four  generations  (that  is, 
by  pollen  of  the  same  form,  but  taken  from  a  distinct 
plant)  and  strict  self-fertilisation.  But  it  is  probable 
that  these  two  processes  do  not  differ  so  essentially  as 
at  first  appears  to  be  the  case.  In  the  following  ex- 
periment any  doubt  arising  from  illegitimate  fertilisa- 
tion was  completely  eliminated. 

(13.)  Primula  veris.  (Equal-styled,  red-flowered 
variety). — Flowers  on  plants  of  the  second  self-fertilised 
generation  were  crossed  with  pollen  from  a  distinct 
variety  or  fresh  stock,  and  others  were  again  self- 
fertilised.  Crossed  plants  and  plants  of  the  third  self- 
fertilised  generation,  all  of  legitimate  origin,  were 
thus  raised  ;  and  the  former  was  to  the  latter  in  height 
as  100  to  85,  and  in  fertility  (as  judged  by  the  number 
of  capsules  produced,  together  with  the  average  number 
of  seeds)  as  100  to  11. 

Summary  of  the  Measurements  in  Table  G. — This 
table  includes  the  heights  and  often  the  weights  of 
292  plants  derived  from  a  cross  with  a  fresh  stock, 
and  of  305  plants,  either  of  self-fertilised  origin,  or 
derived  from  an  intercross  between  plants  of  the  same 
stock.  These  597  plants  belong  to  thirteen  species 
and  twelve  genera.  The  various  precautions  which 
were  taken  to  ensure  a  fair  comparison  have  already 
been  stated.  If  we  now  look  down  the  right-hand 
column,  in  which  the  mean  height,  weight,  and 
fertility  of  the  plants  derived  from  a  cross  with 
a  fresh  stock   are   represented  by  100,  we  shall  see 


Chap.  VII.  TABLE  0.  269 

by  the  other  figures  how  wonderfully  superior  they 
are  both  to  the  self-fertilised  and  to  the  intercrossed 
plants  of  the  same  stock.  With  respect  to  height  and 
weight,  there  are  only  two  exceptions  to  the  rule, 
namely,  with  Eschscholtzia  and  Petunia,  and  the 
latter  is  probably  no  real  exception.  Nor  do  these 
two  species  offer  an  exception  in  regard  to  fertility, 
for  the  plants  derived  from  the  cross  with  a  fresh  stock 
were  much  more  fertile  than  the  self-fertilised  plants. 
The  difference  between  the  two  sets  of  plants  in  the 
table  is  generally  much  greater  in  fertility  than  in 
height  or  weight.  On  the  other  hand,  with  some  of 
the  species,  as  with  Nicotiana,  there  was  no  difference 
in  fertility  between  the  two  sets,  although  a  great  dif- 
ference in  height  and  weight.  Considering  all  the 
cases  in  this  table,  there  can  be  no  doubt  that  plants 
profit  immensely,  though  in  different  ways,  by  a  cross 
with  a  fresh  stock  or  with  a  distinct  sub-variety.  It 
cannot  be  maintained  that  the  benefit  thus  derived  is 
due  merely  to  the  plants  of  the  fresh  stock  being  per- 
fectly healthy,  whilst  those  which  had  been  long  inter- 
crossed or  self-fertilised  had  become  unhealthy  ;  for  in 
most  cases  there  was  no  appearance  of  such  unhealthi- 
ness,  and  we  shall  see  under  Table  A  that  the  inter- 
crossed plants  of  the  same  stock  are  generally  superior 
to  a  certain  extent  to  the  self-fertilised, — both  lots 
having  been  subjected  to  exactly  the  same  conditions 
and  being  equally  healthy  or  unhealthy. 

We  further  learn  from  Table  C,  that  a  cross  between 
plants  that  have  been  self-fertilised  during  several 
successive  generations  and  kept  all  the  time  under 
nearly  uniform  conditions,  does  not  benefit  the  offspring 
in  the  least  or  only  in  a  very  slight  degree.  Mimulus 
and  the  descendants  of  Ipomcea  named  Hero  offer 
instances  of  this  rule.     Again,  plants  self-fertilised 


270  SUMMARY   OF   MEASUREMENTS.  Chap.  VII. 

during  several  generations  profit  only  to  a  small  extent 
by  a  cross  with  intercrossed  plants  of  the  same  stock 
(as  in  the  case  of  Dianthus),  in  comparison  with  the 
effects  of  a  cross  by  a  fresh  stock.  Plants  of  the  same 
stock  intercrossed  during  several  generations  (as  with 
Petunia)  were  inferior  in  a  marked  manner  in  fertility 
to  those  derived  from  the  corresponding  self-fertilised 
plants  crossed  by  a  fresh  stock.  Lastly,  certain  plants 
which  are  regularly  intercrossed  by  insects  in  a  state 
of  nature,  and  which  were  artificially  crossed  in  each 
succeeding  generation  in  the  course  of  my  experi- 
ments, so  that  they  can  never  or  most  rarely  have 
suffered  any  evil  from  self-fertilisation  (as  with  Esch- 
scholtzia  and  Ipomoea),  nevertheless  profited  greatly 
by  a  cross  with  a  fresh  stock.  These  several  cases 
taken  together  show  us  in  the  clearest  manner  that  it 
is  not  the  mere  crossing  of  any  two  individuals  which 
is  beneficial  to  the  offspring.  The  benefit  thus  derived 
depends  on  the  plants  which  are  united  differing  in  some 
manner,  and  there  can  hardly  be  a  doubt  that  it  is 
in  the  constitution  or  nature  of  the  sexual  elements. 
Anyhow,  it  is  certain  that  the  differences  are  not  of  an 
external  nature,  for  two  plants  which  resemble  each 
other  as  closely  as  the  individuals  of  the  same  species 
ever  do,  profit  in  the  plainest  manner  when  inter- 
crossed, if  their  progenitors  have  been  exposed  during 
several  generations  to  different  conditions.  But  to  this 
latter  subject  I  shall  have  to  recur  in  a  future  chapter. 

Table  A. 

We  will  now  turn  to  our  first  table,  which  re- 
lates to  crossed  and  self-fertilised  plants  of  the  same 
stock.  These  consist  of  fifty-four  species  belonging  to 
thirty  natural  orders.  The  total  number  of  crossed 
plants  of  which  measurements  are  given  is  796,  and 


Chap.  VLL  TABLE   A.  271 

of  self-fertilised  plants  809 ;  that  is  altogether  1,605 
plants.  Some  of  the  species  were  experimented  on 
during  several  successive  generations ;  and  it  should 
be  borne  in  mind  that  in  such  cases  the  crossed  plants 
in  each  generation  were  crossed  with  pollen  from 
another  crossed  plant,  and  the  flowers  on  the  self- 
fertilised  plants  were  almost  always  fertilised  with 
their  own  pollen,  though  sometimes  with  pollen  from 
other  flowers  on  the  same  plant.  The  crossed  plants  thus 
became  more  or  less  closely  inter-related  in  the  later 
generations ;  and  both  lots  were  subjected  in  each  ge- 
neration to  almost  absolutely  the  same  conditions,  and 
to  nearly  the  same  conditions  in  the  successive  gene- 
rations. It  would  have  been  a  better  plan  in  some  re- 
spects if  I  had  always  crossed  some  flowers  either  on  the 
self-fertilised  or  intercrossed  plants  of  each  generation 
with  pollen  from  a  non-related  plant,  grown  under  dif- 
ferent conditions,  as  was  done  with  the  plants  in  Table 
C ;  for  by  this  procedure  I  should  have  learnt  how  much 
the  offspring  became  deteriorated  through  continued 
self-fertilisation  in  the  successive  generations.  As  the 
case  stands,  the  self-fertilised  plants  of  the  successive 
generations  in  Table  A  were  put  into  competition  with 
and  compared  with  intercrossed  plants,  which  were 
probably  deteriorated  in  some  degree  by  being  more 
or  less  inter-related  and  grown  under  similar  conditions. 
Nevertheless,  had  I  always  followed  the  plan  in  Table 
0,  I  should  not  have  discovered  the  important  fact 
that,  although  a  cross  between  plants  which  are  rather 
closely  related  and  which  had  been  subjected  to 
closely  similar  conditions,  gives  during  several  genera- 
tions some  advantage  to  the  offspring,  yet  that  after  a 
time  they  may  be  intercrossed  with  no  advantage  what- 
ever to  the  offspring.  Nor  should  I  have  learnt  that 
the  self-fertilised  plants  of  the  later  generations  might 


272  SUMMARY  OF  MEASUREMENTS.         Chap.  VII. 

be  crossed  with  intercrossed  plants  of  the  same  stock 
with  little  or  no  advantage,  although  they  profited  to 
an  extraordinary  degree  by  a  cross  with  a  fresh  stock. 

With  respect  to  the  greater  number  of  the  plants 
in  Table  A,  nothing  special  need  here  be  said ;  full 
particulars  may  be  found  under  the  head  of  each 
species  by  the  aid  of  the  Index.  The  figures  in  the 
right-hand  column  show  the  mean  height  of  the  self- 
fertilised  plants,  that  of  the  crossed  plants  with  which 
they  competed  being  represented  by  100.  No  notice 
is  here  taken  of  the  few  cases  in  which  crossed  and 
self-fertilised  plants  were  grown  in  the  open  ground, 
so  as  not  to  compete  together.  The  table  includes, 
as  we  have  seen,  plants  belonging  to  fifty-four  species, 
but  as  some  of  these  were  measured  during  several 
successive  generations,  there  are  eighty-three  cases  in 
which  crossed  and  self-fertilised  plants  were  compared. 
As  in  each  generation  the  number  of  plants  which 
were  measured  (given  in  the  table)  was  never  very  large 
and  sometimes  small,  whenever  in  the  right-hand 
column  the  mean  height  of  the  crossed  and  self-fertilised 
plants  is  the  same  within  five  per  cent.,  their  heights 
may  be  considered  as  practically  equal.  Of  such  cases, 
that  is,  of  self-fertilised  plants  of  which  the  mean 
height  is  expressed  by  figures  between  95  and  105, 
there  are  eighteen,  either  in  some  one  or  all  the  gene- 
rations. There  are  eight  cases  in  which  the  self- 
fertilised  plants  exceed  the  crossed  by  above  five  per 
cent.,  as  shown  by  the  figures  in  the  right-hand  column 
being  above  105.  Lastly,  there  are  fifty-seven  cases 
in  which  the  crossed  plants  exceed  the  self-fertilised  in 
a  ratio  of  at  least  100  to  95,  and  generally  in  a  much 
higher  degree. 

If  the  relative  heights  of  the  crossed  and  self-fertilised 
plants  had  been  due  to  mere  chance,  there  would  have 


Chap.  VII.  TABLE  A.  273 

been  about  as  many  cases  of  self-fertilised  plants 
exceeding  the  crossed  in  height  by  above  five  per  cent. 
as  of  the  crossed  thus  exceeding  the  self-fertilised ;  but 
we  see  that  of  the  latter  there  are  fifty-seven  cases,  and 
of  the  former  only  eight  cases ;  so  that  the  cases  in 
which  the  crossed  plants  exceed  in  height  the  self- 
fertilised  in  the  above  proportion  are  more  than  seven 
times  as  numerous  as  those  in  which  the  self-fertilised 
exceed  the  crossed  in  the  same  proportion.  For  our 
special  purpose  of  comparing  the  powers  of  growth 
of  crossed  and  self-fertilised  plants,  it  may  be  said 
that  in  fifty-seven  cases  the  crossed  plants  exceeded 
the  self-fertilised  by  more  than  five  per  cent.,  and  that 
in  twenty-six  cases  (18  +  8)  they  did  not  thus  exceed 
them.  But  we  shall  now  show  that  in  several  of  these 
twenty-six  cases  the  crossed  plants  had  a  decided  ad- 
vantage over  the  self-fertilised  in  other  respects,  though 
not  in  height ;  that  in  other  cases  the  mean  heights 
are  not  trustworthy,  owing  to  too  few  plants  having 
been  measured,  or  to  their  having  grown  unequally 
from  being  unhealthy,  or  to  both  causes  combined. 
Nevertheless,  as  these  cases  are  opposed  to  my  general 
conclusion  I  have  felt  bound  to  give  them.  Lastly,  the 
cause  of  the  crossed  plants  having  no  advantage  over 
the  self-fertilised  can  be  explained  in  some  other  cases. 
Thus  a  very  small  residue  is  left  in  which  the  self- 
fertilised  plants  appear,  as  far  as  my  experiments 
serve,  to  be  really  equal  or  superior  to  the  crossed 
plants. 

We  will  now  consider  in  some  little  detail  the  eigh- 
teen cases  in  which  the  self-fertilised  plants  equalled 
in  average  height  the  crossed  plants  within  five  per 
cent. ;  and  the  eight  cases  in  which  the  self-fertilised 
plants  exceeded  in  average  height  the  crossed  plants 
by  above  five  per  cent. ;  making  altogether  twenty-six 


274  SUMMARY  OF  MEASUREMENTS.         Chap.  YIL 

cases  in  which  the  crossed  plants  were  not  taller  than 
the  self-fertilised  plants  in  any  marked  degree. 

(1.)  Diantlius  caryophyllus  (third  generation). — This  plant  was 
experimented  on  during  four  generations,  in  three  of  which  the 
crossed  plants  exceeded  in  height  the  self-fertilised  generally  by 
much  more  than  five  per  cent. ;  and  we  have  seen  under  Table 
C  that  the  offspring  from  the  plants  of  the  third  self-fertilised 
generation  crossed  by  a  fresh  stock  profited  in  height  and  fer- 
tility to  an  extraordinary  degree.  But  in  this  third  generation 
the  crossed  plants  of  the  same  stock  were  in  height  to  the  self- 
fertilised  only  as  100  to  99,  that  is,  they  were  practically  equal. 
Nevertheless,  when  the  eight  crossed  and  eight  self-fertilised 
plants  were  cut  down  and  weighed,  the  former  were  to  the  latter 
in  weight  as  100  to  49 !  There  can  therefore  be  not  the  least 
doubt  that  the  crossed  plants  of  this  species  are  greatly  superior 
in  vigour  and  luxuriance  to  the  self-fertilised ;  and  what  was  the 
cause  of  the  self-fertilised  plants  of  the  third  generation,  though 
so  light  and  thin,  growing  up  so  as  almost  to  equal  the  crossed 
in  height,  I  cannot  explain. 

(2.)  Lobelia  fulgens  (first  generation). — The  crossed  plants  of 
this  generation  were  much  inferior  in  height  to  the  self-fertilised, 
in  the  proportion  of  100  to  127.  Although  only  two  pairs  were 
measured,  which  is  obviously  much  too  few  to  be  trusted, 
yet  from  other  evidence  given  under  the  head  of  this  species, 
it  is  certain  that  the  self-fertilised  plants  were  very  much 
more  vigorous  than  the  crossed.  As  I  used  pollen  of  unequal 
maturity  for  crossing  and  self-fertilising  the  parent-plants,  it  is 
possible  that  the  great  difference  in  the  growth  of  their  offspring 
may  have  been  due  to  this  cause.  In  the  next  generation  this 
source  of  error  was  avoided,  and  many  more  plants  were  raised, 
and  now  the  average  height  of  the  twenty-three  crossed  plants 
was  to  that  of  the  twenty-three  self-fertilised  plants  as  100  to  91. 
"We  can  therefore  hardly  doubt  that  a  cross  is  beneficial  to  this 
species. 

(3.)  Petunia  violacea  (third  generation'). — Eight  crossed  plants 
were  to  eight  self-fertilised  of  the  third  generation  in  average 
height  as  100  to  131;  and  at  an  early  age  the  crossed  were 
inferior  even  in  a  still  higher  degree.  But  it  is  a  remarkable 
fact  that  in  one  pot  in  which  plants  of  both  lots  grew  extremely 
crowded,  the  crossed  were  thrice  as  tall  as  the  self-fertilised.  As 
in  the  two  preceding  and  two  succeeding  generations,  as  well  as 


Chap.  Vn.  TABLE  A.  275 

with  plants  raised  by  a  cross  with  a  fresh  stock,  the  crossed 
greatly  exceeded  the  self-fertilised  in  height,  weight,  and  fertility 
(when  these  two  latter  points  were  attended  to),  the  present  case 
must  be  looked  at  as  an  anomaly  not  affecting  the  general  rule. 
The  most  probable  explanation  is  that  the  seeds  from  which 
the.  crossed  plants  of  the  third  generation  were  raised 
were  not  well  ripened;  for  I  have  observed  an  analogous  case 
with  Iberis.  Self-fertilised  seedlings  of  this  latter  plant,  which 
were  known  to  have  been  produced  from  seeds  not  well  matured, 
grew  from  the  first  much  more  quickly  than  the  crossed  plants, 
which  were  raised  from  better  matured  seeds ;  so  that  having 
thus  once  got  a  great  start  they  were  enabled  ever  afterwards  to 
retain  their  advantage.  Some  of  these  same  seeds  of  the  Iberis 
were  sown  on  the  opposite  sides  of  pots  filled  with  burnt  earth 
and  pure  sand,  not  containing  any  organic  matter ;  and  now  the 
young  crossed  seedlings  grew  during  their  short  life  to  double 
the  height  of  the  self-fertilised,  in  the  same  manner  as  occurred 
with  the  above  two  sets  of  seedlings  of  Petunia  which  were  much 
crowded  and  thus  exposed  to  very  unfavourable  conditions.  We 
have  seen  also  in  the  eighth  generation  of  Ipomoea  that  self- 
fertilised  seedlings  raised  from  unhealthy  parents  grew  at  first 
very  much  more  quickly  than  the  crossed  seedlings,  so  that  they 
were  for  a  long  time  much  taller,  though  ultimately  beaten  by 
them. 

(4,  5,  6.)  Eschscholtzia  californica. — Four  sets  of  measure- 
ments are  given  in  Table  A.  In  one  of  these  the  crossed  plants 
exceed  the  self-fertilised  in  average  height,  so  that  this  is  not 
one  of  the  exceptions  here  to  be  considered.  In  two  other 
cases  the  crossed  equalled  the  self-fertilised  in  height  within  five 
per  cent. ;  and  in  the  fourth  case  the  self-fertilised  exceeded  the 
crossed  by  above  this  limit.  We  have  seen  in  Table  C  that  the 
whole  advantage  of  a  cross  by  a  fresh  stock  is  confined  to  ferti- 
lity, and  so  it  was  with  the  intercrossed  plants  of  the  same  stock 
compared  with  the  self-fertilised,  for  the  former  were  in  fertility 
to  the  latter  as  100  to  89.  The  intercrossed  plants  thus  have  at 
least  one  important  advantage  over  the  self-fertilised.  Moreover, 
the  flowers  on  the  parent-plants  when  fertilised  with  pollen  from 
another  individual  of  the  same  stock  yield  far  more  seeds  than 
when  self-fertilised ;  the  flowers  in  this  latter  case  being  often 
quite  sterile.  We  may  therefore  conclude  that  a  cross  does  some 
good,  though  it  does  not  give  to  the  crossed  seedlings  increased 
powers  of  growth. 


276  SUMMAEY  OF   MEASUREMENTS.         Chap.  VII. 

(7.)  Viscaria  oculata. — The  average  height  of  the  fifteen  inter- 
crossed plants  to  that  of  the  fifteen  self-fertilised  plants  was  only 
as  100  to  97 ;  but  the  former  produced  many  more  capsules  than 
the  latter,  in  the  ratio  of  100  to  77.  Moreover,  the  flowers  on  the 
parent-plants  which  were  crossed  and  self-fertilised,  yielded  seeds 
on  one  occasion  in  the  proportion  of  100  to  38,  and  on  a  second 
occasion  in  the  proportion  of  100  to  58.  So  that  there  can  be 
no  doubt  about  tne  beneficial  effects  of  a  cross,  although  the 
mean  height  of  the  crossed  plants  was  only  three  per  cent,  above 
that  of  the  self-fertilised  plants. 

(8.)  Specularia  speculum. — Only  the  four  tallest  of  the  crossed 
and  the  four  tallest  of  the  self-fertilised  plants,  growing  in  four 
pots,  were  measured ;  and  the  former  were  to  the  latter  in  height 
as  100  to  98.  In  all  four  pots  a  crossed  plant  flowered  before 
any  one  of  the  self-fertilised  plants,  and  this  is  usually  a  safe 
indication  of  some  real  superiority  in  the  crossed  plants.  The 
flowers  on  the  parent- plants  which  were  crossed  with  pollen  from 
another  plant  yielded  seeds  compared  with  the  self-fertilised 
flowers  in  the  ratio  of  100  to  72.  We  may  therefore  draw  the 
same  conclusion  as  in  the  last  case  with  respect  to  a  cross  being 
decidedly  beneficial. 

(9.)  Borago  officinalis, — Only  four  crossed  and  four  self- 
fertilised  plants  were  raised  and  measured,  and  the  former  were 
to  the  latter  in  height  as  100  to  102.  So  small  a  number  of 
measurements  ought  never  to  be  trusted ;  and  in  the  present  in- 
stance the  advantage  of  the  self-fertilised  over  the  crossed  plants 
depended  almost  entirely  on  one  of  the  self- fertilised  plants 
having  grown  to  an  unusual  height.  All  four  crossed  plants 
flowered  before  their  self-fertilised  opponents.  The  cross- 
fertilised  flowers  on  the  parent-plants  in  comparison  with  the 
self-fertilised  flowers  yielded  seeds  in  the  proportion  of  100  to  60. 
So  that  here  again  we  may  draw  the  same  conclusion  as  in  the 
two  last  cases. 

(10.)  Passiflora  gracilis. — Only  two  crossed  and  two  self- 
fertilised  plants  were  raised ;  and  the  former  were  to  the  latter  in 
height  as  100  to  104.  On  the  other  hand,  fruits  from  the  cross- 
fertilised  flowers  on  the  parent-plants  contained  seeds  in  number, 
compared  with  those  from  the  self-fertilised  flowers,  in  the  pro- 
portion of  100  to  85. 

(11.)  Phaseolus  multiflorus. — The  five  crossed  plants  were  to 
the  five  self-fertilised  in  height  as  100  to  96.  Although  the 
crossed  plants  were  thus  only  four  per  cent,  taller  than  the 


Chap.  VII.  TABLE   A.  277 

self-fertilised,  they  flowered  in  both  pots  before  them.  It  is 
therefore  probable  that  they  had  some  real  advantage  over  the 
self-fertilised  plants. 

(12.)  Adonis  cestivalis. — The  four  crossed  plants  were  almost 
exactly  equal  in  height  to  the  four  self-fertilised  plants,  but  as 
so  few  plants  were  measured,  and  as  these  were  all  "  miserably 
unhealthy,"  nothing  can  be  inferred  with  safety  with  respect  to 
their  relative  heights. 

(13.)  Bartonia  aurea. — The  eight  crossed  plants  were  to  the 
eight  self-fertilised  in  height  as  100  to  107.  This  number  of 
plants,  considering  the  care  with  which  they  were  raised  and 
compared,  ought  to  have  given  a  trustworthy  result.  But  from 
some  unknown  cause  they  grew  very  unequally,  and  they  be- 
came so  unhealthy  that  only  three  of  the  crossed  and  three 
of  the  self-fertilised  plants  set  any  seeds,  and  these  few  in 
number.  Under  these  circumstances  the  mean  height  of  neither 
lot  can  be  trusted,  and  the  experiment  is  valueless.  The  cross- 
fertilised  flowers  on  the  parent-plants  yielded  rather  more  seeds 
than  the  self-fertilised  flowers. 

(14.)  Thunhergia  alata. — The  six  crossed  plants  were  to  the 
six  self-fertilised  in  height  as  100  to  108.  Here  the  self-fertilised 
plants  seem  to  have  a  decided  advantage ;  but  both .  lots  grew 
unequally,  some  of  the  plants  in  both  being  more  than  twice  as 
tall  as  others.  The  parent-plants  also  were  in  an  odd  semi- 
sterile  condition.  Under  these  circumstances  the  superiority  of 
the  self-fertilised  plants  cannot  be  fully  trusted. 

(15.)  Nolana prostrata. — The  five  crossed  plants  were  to  the  five 
self-fertilised  in  height  as  100  to  105 ;  so  that  the  latter  seem 
here  to  have  a  small  but  decided  advantage.  On  the  other  hand, 
the  flowers  on  the  parent-plants  which  were  cross-fertilised 
produced  very  many  more  capsules  than  the  self-fertilised  flowers, 
in  the  ratio  of  100  to  21 ;  and  the  seeds  which  the  former  con- 
tained were  heavier  than  an  equal  number  from  the  self -fertilised 
capsules  in  the  ratio  of  100  to  82. 

(16.)  Hibiscus  africanus. — Only  four  pairs  were  raised,  and  the 
crossed  were  to  the  self-fertilised  in  height  as  100  to  109. 
Excepting  that  too  few  plants  were  measured,  I  know  of  nothing 
else  to  cause  distrust  in  the  result.  The  cross-fertilised 
flowers  on  the  parent-plants  were,  on  the  other  hand,  rather 
more  productive  than  the  self-fertilised  flowers. 

(17.)  Apium  petroselinum. — A  few  plants  (number  not  re- 
corded) derived  from  flowers  believed  to  have  been  crossed  by 


278  SUMMAEY   OP   MEASUKEMENTS.         Chap.  VII. 

insects  and  a  few  self-fertilised  plants  were  grown  on  the  opposite 
sides  of  four  pots.  They  attained  to  a  nearly  equal  height,  the 
crossed  having  a  very  slight  advantage. 

(18.)  Vandellia  nummularifolia. — Twenty  crossed  plants  raised 
from  the  seeds  of  perfect  flowers  were  to  twenty  self-fertilised 
plants,  likewise  raised  from  the  seeds  of  perfect  flowers,  in  height 
as  100  to  99.  The  experiment  was  repeated,  with  the  sole 
difference  that  the  plants  were  allowed  to  grow  more  crowded ; 
and  now  the  twenty-four  tallest  of  the  crossed  plants  were  to 
the  twenty-four  tallest  self-fertilised  plants  in  height  as  100  to 
94,  and  in  weight  as  100  to  97.  Moreover,  a  larger  number  of  the 
crossed  than  of  the  self-fertilised  plants  grew  to  a  moderate 
height.  The  above-mentioned  twenty  crossed  plants  were  also 
grown  in  competition  with  twenty  self-fertilised  plants  raised 
from  the  closed  or  cleistogene  flowers,  and  their  heights  were  as 
100  to  94.  Therefore  had  it  not  been  for  the  first  trial,  in  which 
the  crossed  plants  were  to  the  self-fertilised  in  height  only  as 
100  to  99,  this  species  might  have  been  classed  with  those  in 
which  the  crossed  plants  exceed  the  self-fertilised  by  above  five 
per  cent.  On  the  other  hand,  the  crossed  plants  in  the  second 
trial  bore  fewer  capsules,  and  these  contained  fewer  seeds,  than 
did  the  self- fertilised  plants,  all  the  capsules  having  been 
produced  by  cleistogene  flowers.  The  whole  case  therefore  must 
be  left  doubtful. 

(19.)  Pisum  sativum  (common  pea). — Four  plants  derived  from 
a  cross  between  individuals  of  the  same  variety  were  in  height 
to  four  self- fertilised  plants  belonging  to  the  same  variety  as  100 
to  115.  Although  this  cross  did  no  good,  we  have  seen  under 
Table  C  that  a  cross  between  distinct  varieties  adds  greatly  to 
the  height  and  vigour  of  the  offspring ;  and  it  was  there  explained 
that  the  fact  of  a  cross  between  the  individuals  of  the  same  variety 
not  being  beneficial,  is  almost  certainly  due  to  their  having  been 
self-fertilised  for  many  generations,  and  in  each  generation 
grown  under  nearly  similar  conditions. 

(20,  21,  22.)  Canna  warscewiczi. — Plants  belonging  to  three 
generations  were  observed,  and  in  all  of  three  the  crossed  were 
approximately  equal  to  the  self-fertilised ;  the  average  height  of 
the  thirty- four  crossed  plants  being  to  that  of  the  same  number 
of  self-fertilised  plants  as  100  to  101.  Therefore  the  crossed 
plants  had  no  advantage  over  the  self- fertilised ;  and  it  is  pro- 
bable that  the  same  explanation  here  holds  good  as  in  the  case 
of  Pisum  sativum ;  for  the  flowers  of  this  Canna  are  perfectly 


Chap.  VII.  TABLE   A.  279 

self-fertile,  and  were  never  seen  to  be  visited  by  insects  in  the 
hothouse,  so  as  to  be  crossed  by  them.  This  plant,  moreover, 
has  been  cultivated  under  glass  for  several  generations  in  pots, 
and  therefore  under  nearly  uniform  conditions.  The  capsules 
produced  by  the  cross-fertilised  flowers  on  the  above  thirty-four 
crossed  plants  contained  more  seeds  than  did  the  capsules 
produced  by  the  self-fertilised  flowers  on  the  self-fertilised  plants, 
in  the  proportion  of  100  to  85 ;  so  that  in  this  respect  crossing 
was  beneficial. 

(23.)  Primula  sinensis. — The  offspring  of  plants,  some  of 
which  were  legitimately  and  others  illegitimately  fertilised  with 
pollen  from  a  distinct  plant,  were  almost  exactly  of  the  same 
height  as  the  offspring  of  self-fertilised  plants ;  but  the  former 
with  rare  exceptions  flowered  before  the  latter.  I  have  shown 
in  my  paper  on  dimorphic  plants  that  this  species  is  commonly 
raised  in  England  from  self-fertilised  seed,  and  the  plants  from 
having  been  cultivated  in  pots  have  been  subjected  to  nearly 
uniform  conditions.  Moreover,  many  of  them  are  now  varying 
and  changing  their  character,  so  as  to  become  in  a  greater  or 
less  degree  equal-styled,  and  in  consequence  highly  self-fertile. 
Therefore  I  believe  that  the  cause  of  the  crossed  plants  not 
exceeding  in  height  the  self-fertilised  is  the  same  as  in  the  two 
previous  cases  of  Pisum  sativum  and  Canna. 

(24,  25,  26.)  Nicotiana  tabacum. — Four  sets  of  measurements 
were  made ;  in  one,  the  self-fertilised  plants  greatly  exceeded  in 
height  the  crossed,  in  two  others  they  were  approximately  equal 
to  the  crossed,  and  in  the  fourth  were  beaten  by  them ;  but  this 
latter  case  does  not  here  concern  us.  The  individual  plants 
differ  in  constitution,  so  that  the  descendants  of  some  profit  by 
their  parents  having  been  intercrossed,  whilst  others  do  not. 
Taking  all  three  generations  together,  the  twenty-seven  crossed 
plants  were  in  height  to  the  twenty-seven  self-fertilised  plants  as 
100  to  96.  This  excess  of  height  in  the  crossed  plants,  is  so 
small  compared  with  that  displayed  by  the  offspring  from  the 
same  mother-plants  when  crossed  by  a  slightly  different  variety, 
that  we  may  suspect  (as  explained  under  Table  C)  that  most  of 
the  individuals  belonging  to  the  variety  which  served  as  the 
mother-plants  in  my  experiments,  had  acquired  a  nearly  similar 
constitution,  so  as  not  to  profit  by  being  mutually  intercrossed. 

Reviewing   these   twenty-six    cases,   in   which   the 

crossed  plants  either  do  not  exceed  the  self-fertilised 
13 


280  SUMMAEY   OF   MEASUREMENTS.  Chap.  VIL 

by  above  five  per  cent,  in  height,  or  are  inferior  to 
thein,  we  may  conclude  that  much  the  greater  number 
of  the  cases  do  not  form  real  exceptions  to  the  rule, 
— that  a  cross  between  two  plants,  unless  these  have 
been  self-fertilised  and  exposed  to  nearly  the  same 
conditions  for  many  generations,  gives  a  great 
advantage  of  some  kind  to  the  offspring.  Of  the 
twenty-six  cases,  at  least  two,  namely,  those  of  Adonis 
and  Bartonia,  may  be  wholly  excluded,  as  the  trials 
were  worthless  from  the  extreme  unhealthiness  of  the 
plants.  In  twelve  other  cases  (three  trials  with  Esch- 
scholtzia  here  included)  the  crossed  plants  either  were 
superior  in  height  to  the  self-fertilised  in  all  the  other 
generations  excepting  the  one  in  question,  or  they 
showed  their  superiority  in  some  different  manner,  as 
in  weight,  fertility,  or  in  flowering  first ;  or  again,  the 
cross-fertilised  flowers  on  the  mother-plant  were  much 
more  productive  of  seed  than  the  self-fertilised. 

Deducting  these  fourteen  cases,  there  remain  twelve 
in  which  the  crossed  plants  show  no  well-marked 
advantage  over  the  self-fertilised.  On  the  other  hand, 
we  have  seen  that  there  are  fifty-seven  cases  in  which 
the  crossed  plants  exceed  the  self-fertilised  in  height 
by  at  least  five  per  cent.,  and  generally  in  a  much 
higher  degree.  But  even  in  the  twelve  cases  just 
referred  to,  the  want  of  any  advantage  on  the  crossed 
side  is  far  from  certain :  with  Thunbergia  the  parent- 
plants  were  in  an  odd  semi-sterile  condition,  and  the 
offspring  grew  very  unequally;  with  Hibiscus  and 
Apium  much  too  few  plants  were  raised  for  the  measure- 
ments to  be  trusted,  and  the  cross-fertilised  flowers  of 
Hibiscus  produced  rather  more  seed  than  did  the  self- 
fertilised  ;  with  Yandellia  the  crossed  plants  were  a 
little  taller  and  heavier  than  the  self-fertilised,  but  as 
they  were  less  fertile  the  case  must  be  left  doubtful. 


Chap.  VII.  TABLE    A..  281 

Lastly,  with  Pisuni,  Primula,  the  three  generations  of 
Canna,  and  the  three  of  Nicotiana  (-nhich  together 
complete  the  twelve  cases),  a  cross  between  two  plants 
certainly  did  no  good  or  very  little  good  to  the  off- 
spring ;  but  we  have  reason  to  believe  that  this  is  the 
result  of  these  plants  having  been  self-fertilised  and 
cultivated  under  nearly  uniform  conditions  for  several 
generations.  The  same  result  followed  with  the  experi- 
mental plants  of  Ipomoea  and  Mimulus,  and  to  a  certain 
extent  with  some  other  species,  which  had  been  inten- 
tionally treated  by  me  in  this  manner;  yet  we  know  that 
these  species  in  their  normal  condition  profit  greatly  by 
being  intercrossed.  There  is,  therefore,  not  a  single 
case  in  Table  A  which  affords  decisive  evidence  against 
the  rule  that  a  cross  between  plants,  the  progenitors  of 
which  have  been  subjected  to  somewhat  diversified 
conditions,  is  beneficial  to  the  offspring.  This  is  a 
surprising  conclusion,  for  from  the  analogy  of  domesti- 
cated animals  it  could  not  have  been  anticipated,  that 
the  good  effects  of  crossing  or  the  evil  effects  of  self- 
fertilisation  would  have  been  perceptible  until  the 
plants  had  been  thus  treated  for  several  generations. 

The  results  given  in  Table  A  may  be  looked  at 
under  another  point  of  view.  Hitherto  each  genera- 
tion has  been  considered  as  a  separate  case,  of  which 
there  are  eighty-three  ;  and  this  no  doubt  is  the  more 
correct  method  of  comparing  the  crossed  and  self- 
fertilised  plants. 

But  in  those  cases  in  which  plants  of  the  same 
species  were  observed  during  several  generations,  a 
general  average  of  their  heights  in  all  the  generations 
together  may  be  made ;  and  such  averages  are 
given  in  Table  A ;  for  instance,  under  Ipomoea  the 
general  average  for  the  plants  of  all  ten  generations 
is  as  100  for  the  crossed,  to  77  for  the  self-fertilised 


282  SUMMARY   OF   MEASUREMENTS.         Chap.  VII. 

plants.  This  having  been  done  in  each  case  in  which 
more  than  one  generation  was  raised,  it  is  easy  to 
calculate  the  average  of  the  average  heights  of  the 
crossed  and  self-fertilised  plants  of  all  the  species 
included  in  Table  A.  It  should  however  be  observed 
that  as  only  a  few  plants  of  some  species,  whilst  a 
considerable  number  of  others,  were  measured,  the 
value  of  the  mean  or  average  heights  of  the  several 
species  is  very  different.  Subject  to  this  source  of 
error,  it  may  be  worth  while  to  give  the  mean  of  the 
mean  heights  of  the  fifty-four  species  in  Table  A ;  and 
iihe  result  is,  calling  the  mean  of  the  mean  heights 
of  the  crossed  plants  100,  that  of  the  self-fertilised 
plants  is  87.  But  it  is  a  better  plan  to  divide  the 
fifty-four  species  into  three  groups,  as  was  done  with 
the  previously  given  eighty-three  cases.  The  first 
group  consists  of  species  of  which  the  mean  heights 
of  the  self-fertilised  plants  are  within  five  per  cent, 
of  100 ;  so  that  the  crossed  and  self-fertilised  plants 
are  approximately  equal ;  and  of  such  species  there 
are  twelve  about  which  nothing  need  be  said,  the 
mean  of  the  mean  heights  of  the  self-fertilised  being 
of  course  very  nearly  100,  or  exactly  99*58.  The 
second  group  consists  of  the  species,  thirty-seven  in 
number,  of  which  the  mean  heights  of  the  crossed 
plants  exceed  that  of  the  self-fertilised  plants  by 
more  than  five  per  cent. ;  and  the  mean  of  their 
mean  heights  is  to  that  of  the  self-fertilised  plants 
as  100  to  78.  The  third  group  consists  of  the  species, 
only  five  in  number,  of  which  the  mean  heights  of 
the  self-fertilised  plants  exceed  that  of  the  crossed  by 
more  than  five  per  cent. ;  and  here  the  mean  of  the 
mean  heights  of  the  crossed  plants  is  to  that  of  the 
self-fertilised  as  100  to  109.  Therefore  if  we  exclude 
the  species  which  are  approximately  equal,  there  are 


Chap.  VII.  TABLE  B.  283 

thirty-seven  species  in  which  the  mean  of  the  mean 
heights  of  the  crossed  plants  exceeds  that  of  the  self- 
fertilised  by  twenty -two  per  cent. ;  whereas  there  are 
only  five  species  in  which  the  mean  of  the  mean  heights 
of  the  self-fertilised  plants  exceeds  that  of  the  crossed, 
and  this  only  by  nine  per  cent. 

The  truth  of  the  conclusion — that  the  good  effects  of 
a  cross  depend  on  the  plants  having  been  subjected 
to  different  conditions  or  to  their  belonging  to  differ- 
ent varieties,  in  both  of  which  cases  they  would  almost 
certainly  differ  somewhat  in  constitution — is  supported 
by  a  comparison  of  the  Tables  A  and  C.  The  latter 
table  gives  the  results  of  crossing  plants  with  a  fresh 
stock  or  with  a  distinct  variety  ;  and  the  superiority  of 
the  crossed  offspring  over  the  self-fertilised  is  here 
much  more  general  and  much  more  strongly  marked 
than  in  Table  A,  in  which  plants  of  the  same  stock 
were  crossed.  We  have  just  seen  that  the  mean  of  the 
mean  heights  of  the  crossed  plants  of  the  whole  fifty- 
four  species  in  Table  A  is  to  that  of  the  self-fertilised 
plants  as  100  to  87 ;  whereas  the  mean  of  the  mean 
heights  of  the  plants  crossed  by  a  fresh  stock  is  to  that 
of  the  self-fertilised  in  Table  C  as  100  to  74.  So  that 
the  crossed  plants  beat  the  self-fertilised  plants  by 
thirteen  per  cent,  in  Table  A,  and  by  twenty-six  per 
cent.,  or  double  as  much,  in  Table  C,  which  includes 
the  results  of  a  cross  by  a  fresh  stock. 

Table  B. 

A  few  words  must  be  added  on  the  weights  of 
the  crossed  plants  of  the  same  stock,  in  comparison 
with  the  self-fertilised.  Eleven  cases  are  given  in 
Table  B,  relating  to  eight  species.  The  number  of 
plants  which  were  weighed  is  shown  in  the  two  left 
columns,   and   their    relative    weights    in   the    right 


284  SUMMARY  OF   MEASUREMENTS.         Chap.  VII. 

column,  that  of  the  crossed  plants  being  taken  as 
100.  A  few  other  cases  have  already  been  recorded 
in  Table  C  in  reference  to  plants  crossed  by  a  fresh 
stock.  I  regret  that  more  trials  of  this  kind  were  not 
made,  as  the  evidence  of  the  superiority  of  the  crossed 
over  the  self-fertilised  plants  is  thus  shown  in  a  more 
conclusive  manner  than  by  their  relative  heights.  But 
this  plan  was  not  thought  of  until  a  rather  late  period, 
and  there  were  difficulties  in  the  way,  as  the  seeds 
had  to  be  collected  when  ripe,  by  which  time  the  plants 
had  often  begun  to  wither.  In  only  one  out  of  the 
eleven  cases  in  Table  B,  that  of  Eschscholtzia,  do  the 
self- fertilised  plants  exceed  the  crossed  in  weight ;  and 
we  have  already  seen  they  are  likewise  superior  to  them 
in  height,  though  inferior  in  fertility,  the  whole  ad- 
vantage of  a  cross  being  here  confined  to  the  repro- 
ductive system.  With  Vandellia  the  crossed  plants 
were  a  little  heavier,  as  they  were  also  a  little  taller 
than  the  self- fertilised ;  but  as  a  greater  number  of 
more  productive  capsules,  were  produced  by  the  cleis- 
togene  flowers  on  the  self-fertilised  plants  than  by 
those  on  the  crossed  plants,  the  case  must  be  left,  as 
remarked  under  Table  A,  altogether  doubtful.  The 
crossed  and  self-fertilised  offspring  from  a  partially 
self-sterile  plant  of  Reseda  odorata  were  almost  equal 
in  weight,  though  not  in  height.  In  the  remaining 
eight  cases,  the  crossed  plants  show  a  wonderful 
superiority  over  the  self-fertilised,  being  more  than 
double  their  weight,  except  in  one  case,  and  here 
the  ratio  is  as  high  as  100  to  67.  The  results  thus 
deduced  from  the  weights  of  the  plants  confirm  in  a 
striking  manner  the  former  evidence  of  the  beneficial 
effects  of  a  cross  between  two  plants  of  the  same  stock  ; 
and  in  the  few  cases  in  which  plants  derived  from  a 
cross  with  a  fresh  stock  were  weighed,  the  results  are 
similar  or  even  more  striking. 


Chap.  VIII.  CONSTITUTIONAL   VIGOUR.  285 


CHAPTER  Till. 

Difference    between    Crossed    and    Self-fertilised    Plants    in 
Constitutional  Vigour  and  in  other  respects. 

Greater  constitutional  vigour  of  crossed  plants — The  effects  of  great 
crowding — Competition  with  other  kinds  of  plants — Self-fertilised 
plants  more  liable  to  premature  death — Crossed  plants  generally 
flower  before  the  self-fertilised —Negative  effects  of  intercrossing 
flowers  on  the  same  plant — Cases  described — Transmission  of  the 
good  effects  of  a  cross  to  later  generations — Effects  of  crossing 
plants  of  closely  related  parentage — Uniform  colour  of  the  flowers 
on  plants  self-fertilised  during  several  generations  and  cultivated 
under  similar  conditions. 

Greater  constitutional  Vigour  of  crossed  Plants. — As  in 
almost  all  my  experiments  an  equal  number  of  crossed 
and  self-fertilised  seeds,  or  more  commonly  seedlings 
just  beginning  to  sprout,  were  planted  on  the  oppo- 
site sides  of  the  same  pots,  they  had  to  compete 
with  one  another  ;  and  the  greater  height,  weight,  and 
fertility  of  the  crossed  plants  may  be  attributed  to 
their  possessing  greater  innate  constitutional  vigour. 
Generally  the  plants  of  the  two  lots  whilst  very  young 
were  of  equal  height;  but  afterwards  the  crossed 
gained  insensibly  on  their  opponents,  and  this  shows 
that  they  possessed  some  inherent  superiority,  though 
not  displayed  at  a  very  early  period  of  life.  There 
were,  however,  some  conspicuous  exceptions  to  the 
rule  of  the  two  lots  being  at  first  equal  in  height ;  thus 
the  crossed  seedlings  of  the  broom  {Sarothamnus 
scoparius)  when  under  three  inches  in  height  were  more 
than  twice  as  tall  as  the  self-fertilised  plants. 


286  CONSTITUTIONAL  VIGOUR  Chap.  VIII. 

After  the  crossed  or  the  self-fertilised  plants  had 
once  grown  decidedly  taller  than  their  opponents,  a 
still  increasing  advantage  would  tend  to  follow 
from  the  stronger  plants  robbing  the  weaker  ones 
of  nourishment  and  overshadowing  them.  This  was 
evidently  the  case  with  the  crossed  plants  of  Viola  tri- 
color, which  ultimately  quite  overwhelmed  the  self- 
fertilised.  But  that  the  crossed  plants  have  an  inherent 
superiority,  independently  of  competition,  was  some- 
times well  shown  when  both  lots  were  planted 
separately,  not  far  distant  from  one  another,  in  good 
soil  in  the  open  ground.  This  was  likewise  shown  in 
several  cases,  even  with  plants  growing  in  close  compe- 
tition with  one  another,  by  one  of  the  self-fertilised 
plants  exceeding  for  a  time  its  crossed  opponent,  which 
had  been  injured  by  some  accident  or  was  at  first 
sickly,  but  being  ultimately  conquered  by  it.  The 
plants  of  the  eighth  generation  of  Ipomoea  were  raised 
from  small  seeds  produced  by  unhealthy  parents,  and 
the  self-fertilised  plants  grew  at  first  very  rapidly, 
so  that  when  the  plants  of  both  lots  were  about  three 
feet  in  height,  the  mean  height  of  the  crossed  to  that 
of  the  self-fertilised  was  as  100  to  122 ;  when  they 
were  about  six  feet  high  the  two  lots  were  very  nearly 
equal,  but  ultimately  when  between  eight  and  nine  feet 
in  height,  the  crossed  plants  asserted  their  usual 
superiority,  and  were  to  the  self-fertilised  in  height  as 
100  to  85. 

The  constitutional  superiority  of  the  crossed  over  the 
self-fertilised  plants  was  proved  in  another  way  in  the 
third  generation  of  Mimulus,  by  self-fertilised  seeds 
being  sown  on  one  side  of  a  pot,  and  after  a  certain 
interval  of  time  crossed  seeds  on  the  opposite  side.  The 
self-fertilised  seedlings  thus  had  (for  I  ascertained  that 
the  seeds  germinated  simultaneously)  a  clear  advantage 


Chap.  VIII  OF  THE   CROSSED  PLANTS.  287 

over  the  crossed  in  the  start  for  the  race.  Nevertheless 
they  were  easily  beaten  (as  may  be  seen  under  the> 
head  of  Mimulus)  when  the  crossed  seeds  were  sown 
two  whole  days  after  the  self-fertilised.  But  when  the 
interval  was  four  days,  the  two  lots  were  nearly  equal 
throughout  life.  Even  in  this  latter  case  the  crossed 
plants  still  possessed  an  inherent  advantage,  for  after 
both  lots  had  grown  to  their  full  height  they  were 
cut  down,  and  without  being  disturbed  were  transferred 
to  a  larger  pot,  and  when  in  the  ensuing  year  they 
had  again  grown  to  their  full  height  they  were 
measured ;  and  now  the  tallest  crossed  plants  were  to 
the  tallest  self-fertilised  plants  in  height  as  100  to  75, 
and  in  fertility  (i.e.,  by  weight  of  seeds  produced  by  an 
equal  number  of  capsules  from  both  lots)  as  100  to  34. 
My  usual  method  of  proceeding,  namely,  to  plant 
several  pairs  of  crossed  and  self-fertilised  seeds  in  an 
equal  state  of  germination  on  the  opposite  sides  of  the 
same  pots,  so  that  the  plants  were  subjected  to 
moderately  severe  mutual  competition,  was  I  think 
the  best  that  could  have  been  followed,  and  was  a  fair 
test  of  what  occurs  in  a  state  of  nature.  For  plants 
sown  by  nature  generally  come  up  crowded,  and  are 
almost  always  exposed  to  very  severe  competition 
with  one  another  and  with  other  kinds  of  plants.  This 
latter  consideration  led  me  to  make  some  trials,  chiefly 
but  not  exclusively  with  Ipomoea  and  Mimulus,  by 
sowing  crossed  and  self-fertilised  seeds  on  the  opposite 
sides  of  large  pots  in  which  other  plants  had  long  been 
growing,  or  in  the  midst  of  other  plants  out  of  doors. 
The  seedlings  were  thus  subjected  to  very  severe 
competition  with  plants  of  other  kinds;  and  in  all 
such  cases,  the  crossed  seedlings  exhibited  a  great 
superiority  in  their  power  of  growth  over  the  self- 
fertilised. 


288  CONSTITUTIONAL  VIGOUR  Chap.  VIII. 

After  the  germinating  seedlings  had  been  planted 
in  pairs  on  the  opposite  sides  of  several  pots,  the 
remaining  seeds,  whether  or  not  in  a  state  of  germina- 
tion, were  in  most  cases  sown  very  thickly  on  the  two 
sides  of  an  additional  large  pot ;  so  that  the  seedlings 
came  up  extremely  crowded,  and  were  subjected  to 
extremely  severe  competition  and  unfavourable  condi- 
tions. In  such  cases  the  crossed  plants  almost  invari- 
ably showed  a  greater  superiority  over  the  self-fertilised, 
than  did  the  plants  which  grew  in  pairs  in  the  pots. 

Sometimes  crossed  and  self-fertilised  seeds  were 
sown  in  separate  rows  in  the  open  ground,  which  was 
kept  clear  of  weeds ;  so  that  the  seedlings  were  not 
subjected  to  any  competition  with  other  kinds  of 
plants.  Those  however  in  each  row  had  to  struggle 
with  the  adjoining  ones  in  the  same  row.  When  fully 
grown,  several  of  the  tallest  plants  in  each  row  were 
selected,  measured,  and  compared.  The  result  was 
in  several  cases  (but  not  so  invariably  as  might  have 
been  expected)  that  the  crossed  plants  did  not  exceed 
in  height  the  self-fertilised  in  nearly  so  great  a  degree 
as  when  grown  in  pairs  in  the  pots.  Thus  with  the 
plants  of  Digitalis,  which  competed  together  in  pots,  the 
crossed  were  to  the  self-fertilised  in  height  as  100  to 
70 ;  whilst  those  which  were  grown  separately  were  only 
as  100  to  85.  Nearly  the  same  result  was  observed 
with  Brassica.  With  Nicotiana  the  crossed  were  to 
the  self- fertilised  plants  in  height,  when  grown 
extremely  crowded  together  in  pots,  as  100  to  54 ; 
when  grown  much  less  crowded  in  pots  as  100  to  66, 
and  when  grown  in  the  open  ground,  so  as  to  be  sub- 
jected to  but  little  competition,  as  100  to  72.  On  the 
other  hand  with  Zea,  there  was  a  greater  difference  in 
height  between  the  crossed  and  self -fertilised  plants 
growing  out   of  doors,  than  between  the  pairs  which 


Chap.  VIII.  OF  THE  CROSSED  PLANTS.  289 

grew  in  pots  in  the  hothouse;  but  this  may  be 
attributed  to  the  self-fertilised  plants  being  more 
tender,  so  that  they  suffered  more  than  the  crossed, 
when  both  lots  were  exposed  to  a  cold  and  wet  summer. 
Lastly,  with  one  out  of  two  series  of  Reseda  odorata, 
grown  out  of  doors  in  rows,  as  well  as  with  Beta 
vidgaris,  the  crossed  plants  did  not  at  all  exceed  the  self- 
fertilised  in  height,  or  exceeded  them  by  a  mere  trifle. 

The  innate  power  of  the  crossed  plants  to  resist 
unfavourable  conditions  far  better  than  did  the  self- 
fertilised  plants,  was  shown  on  two  occasions  in  a 
curious  manner,  namely,  with  Iberis  and  in  the  third 
generation  of  Petunia,  by  the  great  superiority  in 
height  of  the  crossed  over  the  self-fertilised  seedlings, 
when  both  sets  were  grown  under  extremely  unfavourable 
conditions ;  whereas  owing  to  special  circumstances 
exactly  the  reverse  occurred  with  the  plants  raised  from 
the  same  seeds  and  grown  in  pairs  in  pots.  A  nearly 
analogous  case  was  observed  on  two  other  occasions 
with  plants  of  the  first  generation  of  Nicotiana. 

The  crossed  plants  always  withstood  the  injurious 
effects  of  being  suddenly  removed  into  the  open  air 
after  having  been  kept  in  the  greenhouse  better  than 
did  the  self-fertilised.  On  several  occasions  they  also 
resisted  much  better  cold  and  intemperate  weather. 
This  was  manifestly  the  case  with  some  crossed  and 
self-fertilised  plants  of  Ipomoea,  which  were  suddenly 
moved  from  the  hothouse  to  the  coldest  part  of  a  cool 
greenhouse.  The  offspring  of  plants  of  the  eighth 
self-fertilised  generation  of  Mimulus  crossed  by  a  fresh 
stock,  survived  a  frost  which  killed  every  single  self- 
fertilised  and  intercrossed  plant  of  the  same  old  stock. 
Nearly  the  same  result  followed  with  some  crossed  and 
self-fertilised  plants  of  Viola  tricolor.  Even  the  tips 
of  the  shoots  of  the   crossed   plants  of  Sarothamnus 


290  CONSTITUTIONAL  VIGOUR  Chap.  VI IL 

scoparius  were  not  touched  by  a  very  severe  winter ; 
whereas  all  the  self-fertilised  plants  were  killed  half- 
way down  to  the  ground,  so  that  they  were  not  able  to 
flower  during  the  next  summer.  Young  crossed 
seedlings  of  JSTicotiana  withstood  a  cold  and  wet 
summer  much  better  than  the  self-fertilised  seedlings. 
I  have  met  with  only  one  exception  to  the  rule  of 
crossed  plants  being  hardier  than  the  self-fertilised : 
three  long  rows  of  Eschscholtzia  plants,  consisting  of 
crossed  seedlings  from  a  fresh  stock,  of  intercrossed 
seedlings  of  the  same  stock,  and  of  self-fertilised  ones, 
were  left  unprotected  during  a  severe  winter,  and  all 
perished  except  two  of  the  self-fertilised.  But  this 
case  is  not  so  anomalous  as  it  at  first  appears,  for  it 
should  be  remembered  that  the  self-fertilised  plants 
of  Eschscholtzia  always  grow  taller  and  are  heavier 
than  the  crossed ;  the  whole  benefit  of  a  cross  with  this 
species  being  confined  to  increased  fertility. 

Independently  of  any  external  cause  which  could 
be  detected,  the  self-fertilised  plants  were  more  liable 
to  premature  death  than  were  the  crossed ;  and  this 
seems  to  me  a  curious  fact.  Whilst  the  seedlings 
were  very  young,  if  one  died  its  antagonist  was  pulled 
up  and  thrown  away,  and  I  believe  tha.t  many  more  of 
the  self-fertilised  died  at  this  early  age  than  of  the 
crossed ;  but  I  neglected  to  keep  any  record.  With. 
Beta  vulgaris,  however,  it  is  certain  that  a  large  number 
of  the  self-fertilised  seeds  perished  after  germinating 
beneath  the  ground,  whereas  the  crossed  seeds  sown  at 
the  same  time  did  not  thus  suffer.  When  a  plant 
died  at  a  somewhat  more  advanced  age  the  fact  was 
recorded ;  and  I  find  in  my  notes  that  out  of  several 
hundred  plants,  only  seven  of  the  crossed  died,  whilst 
of  the  self-fertilised  at  least  twenty-nine  were  thus 
lost,  that  is  more  than  four  times  as  many.  Mr.  G-alton, 


Chap.  VIII.  OF   THE   CEOSSED  PLANTS.  291 

after  examining  some  of  my  tables,  remarks  :  "  It  is  very 
evident  that  the  columns  with  the  self-fertilised  plants 
include  the  larger  number  of  exceptionally  small 
plants  ; "  and  the  frequent  presence  of  such  puny  plants 
no  doubt  stands  in  close  relation  with  their  liability  to 
premature  death.  The  self-fertilised  plants  of  Petunia 
completed  their  growth  and  began  to  wither  sooner 
than  did  the  intercrossed  plants ;  and  these  latter 
considerably  before  the  offspring  from  a  cross  with  a 
fresh  stock. 

Period  of  Flowering. — In  some  cases,  as  with  Digitalis, 
Dianthus,  and  Keseda,  a  larger  number  of  the  crossed 
than  of  the  self-fertilised  plants  threw  up  flower-stems ; 
but  this  probably  was  merely  the  result  of  their  greater 
power  of  growth  ;  for  in  the  first  generation  of  Lobelia 
fulgens,  in  which  the  self-fertilised  plants  greatly  ex- 
ceeded in  height  the  crossed  plants,  some  of  the  latter 
failed  to  throw  up  flower-stems.  With  a  large  number 
of  species,  the  crossed  plants  exhibited  a  well-marked 
tendency  to  flower  before  the  self-fertilised  ones 
growing  in  the  same  pots.  It  should  however  be 
remarked  that  no  record  was  kept  of  the  flowering  of 
many  of  the  species ;  and  when  a  record  was  kept, 
the  flowering  of  the  first  plant  in  each  pot  was  alone 
observed,  although  two  or  more  pairs  grew  in  the  same 
pot.  I  will  now  give  three  lists, — one  of  the  species 
in  which  the  first  plant  that  flowered  was  a  crossed 
one, — a  second  in  which  the  first  that  flowered  was  a 
self-fertilised  plant, — and  a  third  of  those  which 
flowered  at  the  same  time. 

Species,  of  which  the  first  Plants  that  flowered  were 
of  Crossed  Parentage. 
Ipomoea  purpurea. — I  record  in  my  notes  that  in  all  ten  genera- 
tions many  of  the  crossed  plants  flowered  before  the  self- 
fertilised  ;  but  no  details  were  kept. 


292  *  PEEIOD   OF  FLOWERING  OF  Chap.  V11I. 

Mimulus  luteus  (First  Generation). — Ten  flowers  on  the  crossed 
plants  were  fully  expanded  before  one  on  the  self-fertilised. 

Mimulus  luteus  (Second  and  Third  Generation). — In  both  these 
generations  a  crossed  plant  flowered  before  one  of  the  self- 
fertilised  in  all  three  pots. 

Mimulus  luteus  (Fifth  Generation). — In  all  three  pots  a  crossed 
plant  flowered  first;  yet  the  self-fertilised  plants,  which 
belonged  to  the  new  tall  variety,  were  in  height  to  the 
crossed  as  126  to  100. 

Mimulus  luteus. — Plants  derived  from  a  cross  with  a  fresh  stock 
as  well  as  the  intercrossed  plants  of  the  old  stock,  flowered 
before  the  self-fertilised  plants  in  nine  out  of  the  ten  pots. 

Salvia  coccinea. — A  crossed  plant  flowered  before  any  one  of  the 
self-fertilised  in  all  three  pots. 

Origanum  vulgare. — During  two  successive  seasons  several 
crossed  plants  flowered  before  the  self-fertilised. 

Brassica  olerucea  (First  Generation). — All  the  crossed  plants 
growing  in  pots  and  in  the  open  ground  flowered  first. 

Brassica  oleracea  (Second  Generation). — A  crossed  plant  in 
three  out  of  the  four  pots  flowered  before  any  one  of  the 
self-fertilised. 

Iheris  umbdlata. — In  both  pots  a  crossed  plant  flowered  first. 

Eschscholtzia  californica. — Plants  derived  from  the  Brazilian 
stock  crossed  by  the  English  stock  flowered  in  five  out  of 
the  nine  pots  first ;  in  four  of  them  a  self-fertilised  plant 
flowered  first ;  and  not  in  one  pot  did  an  intercrossed  plant 
of  the  old  stock  flower  first. 

Viola  tricolor. — A  crossed  plant  in  five  out  of  the  six  pots 
flowered  before  any  one  of  the  self-fertilised. 

Dianthus  caryophyllus  (First  Generation). — In  two  large  beds 
of  plants,  four  of  the  crossed  plants  flowered  before  any  one 
of  the  self-fertilised. 

Dianthus  caryophyllus  (Second  Generation). — In  both  pots  a 
crossed  plant  flowered  first. 

Dianthus  caryophyllus  (Third  Generation). — In  three  out  of 
the  four  pots  a  crossed  plant  flowered  first ;  yet  the  crossed 
were  to  the  self-fertilised  in  height  only  as  100  to  99,  but  in 
weight  as  100  to  49. 

Dianthus  caryophyllus. — Plants  derived  from  a  cross  with  a  fresh 
stock,  and  the  intercrossed  plants  of  the  old  stock,  both 
flowered  before  the  self-fertilised  in  nine  out  of  the  ten  pots. 

Hibiscus  africanus. — In  three  out  of  the  four  joots  a  crossed 


Chap.  VIII.   CEOSSED   AND   SELF-FERTILISED   PLANTS.  293 

plant  flowered  before  any  one  of  the  self-fertilised ;  yet  the 

latter  were  to  the  crossed  in  height  as  109  to  100. 
Tropseolum  minus. — A  crossed  plant  flowered  before  any  one  of 

the  self-fertilised  in  three  out  of  the  four  pots,  and  simul- 
taneously in  the  fourth  pot. 
Limnanthes  douglasii. — A  crossed  plant  flowered  before  any  one 

of  the  self-fertilised  in  four  out  of  the  five  pots. 
Fhaseolus  multiflorus. — In  both  pots  a  crossed  plant  flowered 

first. 
Specularia  speculum. — In  all  four  pots  a  crossed  plant  flowered 

first. 
Lobelia  ramosa  (First  Generation). — In  all  four  pots   a  crossed 

plant  flowered  before  any  one  of  the  self-fertilised. 
Lobelia  ramosa  (Second  Generation). — In  all  four  pots  a  crossed 

plant    flowered    some   days  before    any  one  of   the  self- 
fertilised. 
Nemophila  insignis. — In  four  out  of  the  five  pots  a  crossed  plant 

flowered  first. 
Borago  officinalis. — In  both  pots  a  crossed  plant  flowered  first. 
Petunia  violacea  (Second    Generation). — In    all  three    pots    a 

crossed  plant  flowered  first. 
Nicotiana  tabacum. — A  plant  derived  from  a  cross  with  a  fresh 

stock  flowered  before  any  one  of  the  self-fertilised  plants  of 

the  fourth  generation,  in  fifteen  out  of  the  sixteen  pots. 
Cyclamen  persicum. — Dm'ing  two  successive  seasons  a  crossed 

plant  flowered  some  weeks  before  any  one  of  the  self-fertilised 

in  all  four  pots. 
Primula  veris  (equal-styled  var.). — In  all  three  pots  a  crossed 

plant  flowered  first. 
Primula  sinensis. — In   all  four  pots   plants   derived    from   an 

illegitimate  cross  between  distinct  plants  flowered  before 

any  one  of  the  self-fertilised  plants. 
Primula  sinensis. — A  legitimately  crossed  plant  flowered  before 

any  one  of  the  self-fertilised  plants  in  seven  out  of  the  eight 

pots. 
Fagopyrum  esculentum.. — A  legitimately  crossed  plant  flowered 

from  one  to  two  days  before  any  one  of  the  self-fertilised 

plants  in  all  three  pots. 
Zea  mays. — In  all  four  pots  a  crossed  plant  flowered  first. 
Phalaris  canariensis. — The  crossed  plants  flowered  before  the 

self-fertilised  in  the  open  ground,  but  simultaneously  in  the 

pots. 


294  PBKIOD   OF   FLOWEEING   OF  Chap.  VIII. 

Species,  of  which  the  first  Plants  that  flowered  were  of 
Self -fertilised  Parentage. 

Esclischoltzia  californica  (First  Generation). — The  crossed  plants 
were  at  first  taller  than  the  self-fertilised,  but  on  their  second 
growth  during  the  following  year  the  self-fertilised  exceeded 
the  crossed  in  height,  and  now  they  flowered  first  in  three 
out  of  the  four  pots. 

Lupinus  luteus. — Although  the  crossed  plants  were  to  the  self- 
fertilised  in  height  as  100  to  82 ;  yet  in  all  three  pots  the 
self-fertilised  plants  flowered  first. 

Clarhia  elegans. — Although  the  crossed  plants  were,  as  in  the 
last  case,  to  the  self-fertilised  in  height  as  100  to  82,  yet  in 
the  two  pots  the  self-fertilised  flowered  first. 

Lobelia  fulg ens  (First  Generation). — The  crossed  plants  were  to 
the  self-fertilised  in  height  only  as  100  to  127,  and  the  latter 
flowered  much  before  the  crossed. 

Petunia  violacea  (Third  Generation). — The  crossed  plants  were 
to  the  self-fertilised  in  height  as  100  to  131,  and  in  three 
out  of  the  four  pots  a  self-fertilised  plant  flowered  first ;  in 
the  fourth  pot  simultaneously. 

Petunia  violacea  (Fourth  Generation). — Although  the  crossed 
plants  were  to  the  self-fertilised  in  height  as  100  to  69,  yet 
in  three  out  of  the  five  pots  a  self-fertilised  plant  flowered 
first ;  in  the  fourth  pot  simultaneously,  and  only  in  the  fifth 
did  a  crossed  plant  flower  first. 

Nicotiana  tabacum  (First  Generation). — The  crossed  plants 
were  to  the  self-fertilised  in  height  only  as  100  to  178,  and 
a  self-fertilised  plant  flowered  first  in  all  four  pots. 

Nicotiana  tabacum  (Third  Generation). — The  crossed  plants 
were  to  the  self-fertilised  in  height  as  100  to  101,  and  in 
four  out  of  the  five  pots  a  self-fertilised  plant  flowered  first. 

Canna  warscewiczi. — In  the  three  generations  taken  together  the 
crossed  were  to  the  self-fertilised  in  height  as  100  to  101 ;  in 
the  first  generation  the  self-fertilised  plants  showed  some 
tendency  to  flower  first,  and  in  the  third  generation  they 
flowered  first  in  nine  out  of  the  twelve  pots. 

Species  in  which  the  Crossed  and  Self -fertilised  Plants 
flowered  almost  simidtaneously. 
Mimulus  luteus   (Sixth  Generation). — The  crossed  plants  were 
inferior  in  height  and  vigour  to  the  self-fertilised  plants, 


Chap.  VIII.  CROSSED   AND   SELF-FERTILISED  PLANTS.  295 

which  all  belonged  to  the  new  white-flowered  tall  variety, 
yet  in  only  half  the  pots  did  the  self-fertilised  plants  flower 
first,  and  in  the  other  half  the  crossed  plants. 

Viscaria  oculata.  —The  crossed  plants  were  only  a  little  taller 
than  the  self-fertilised  (viz.,  as  100  to  97),  bnt  con- 
siderably more  fertile,  yet  both  lots  flowered  almost 
simultaneously. 

Lathyrus  odoratus  (Second  Generation). — Although  the  crossed 
plants  were  to  the  self-fertilised  in  height  as  100  to  88,  yet 
there  was  no  marked  difference  in  their  period  of  flowering. 

Lobelia  fulgens  (Second  Generation). — Although  the  crossed 
plants  were  to  the  self-fertilised  in  height  as  100  to  91,  yet 
they  flowered  simultaneously. 

Nicotiana  tabacum  (Third  Generation). — Although  the  crossed 
plants  were  to  the  self-fertilised  in  height  as  100  to  83,  yet 
in  half  the  pots  a  self-fertilised  plant  flowered  first,  and  in 
the  other  half  a  crossed  plant. 

These  three  lists  include  fifty-eight  cases,  in  which 
the  period  of  flowering  of  the  crossed  and  self-fertilised 
plants  was  recorded.  In  forty-four  of  them  a  crossed 
plant  flowered  first  either  in  a  majority  of  the  pots  or 
in  all ;  in  nine  instances  a  self-fertilised  plant  flowered 
first,  and  in  five  the  two  lots  flowered  simultaneously. 
One  of  the  most  striking  cases  is  that  of  Cyclamen,  in 
which  the  crossed  plants  flowered  some  weeks  before 
the  self-fertilised  in  all  four  pots  during  two  seasons. 
In  the  second  generation  of  Lobelia  ramosa,  a  crossed 
plant  flowered  in  all  four  pots  some  days  before  any 
one  of  the  self-fertilised.  Plants  derived  from  a 
cross  with  a  fresh  stock  generally  showed  a  very 
strongly  marked  tendency  to  flower  before  the  self- 
fertilised  and  the  intercrossed  plants  of  the  old  stock  ; 
all  three  lots  growing  in  the  same  pots.  Thus  with 
Mimulus  and  Dianthus,  in  only  one  pot  out  of  ten,  and 
in  Nicotiana  in  only  one  pot  out  of  sixteen,  did  a  self- 
fertilised  plant  flower  before  the  plants  of  the  two  crossed 
kinds, — these  latter  flowering  almost  simultaneously. 


296  PERIOD   OF  FLOWERING  OF  Chap.  VIII. 

A  consideration  of  the  two  first  lists,  especially  of 
the  second  one,  shows  that  a  tendency  to  flower  first  is 
generally  connected  with  greater  power  of  growth,  that 
is,  with  greater  height.  But  there  are  some  remarkable 
exceptions  to  this  rule,  proving  that  some  other  cause 
comes  into  play.  Thus  the  crossed  plants  both  of 
Lujpinus  luteus  and  ClarMa  elegans  were  to  the  self- 
fertilised  plants  in  height  as  100  to  82,  and  yet  the 
latter  flowered  first.  In  the  third  generation  of  Nico- 
tiana,  and  in  all  three  generations  of  Canna,  the 
crossed  and  self-fertilised  plants  were  of  nearly  equal 
height,  yet  the  self-fertilised  tended  to  flower  first. 
On  the  other  hand,  with  Primula  sinensis,  plants 
raised  from  a  cross  between  two  distinct  individuals, 
whether  these  were  legitimately  or  illegitimately 
crossed,  flowered  before  the  illegitimately  self-fertilised 
plants,  although  all  the  plants  were  of  nearly  equal 
height  in  both  cases.  So  it  was  with  respect  to  height 
and  flowering  with  Phaseolus,  Specularia,  and  Borago. 
The  crossed  plants  of  Hibiscus  were  inferior  in  height 
to  the  self-fertilised,  in  the  ratio  of  100  to  109,  and  yet 
they  flowered  before  the  self-fertilised  in  three  out  of 
the  four  pots.  On  the  whole,  there  can  be  no  doubt 
that  the  crossed  plants  exhibit  a  tendency  to  flower 
before  the  self-fertilised,  almost  though  not  quite  so 
strongly  marked  as  to  grow  to  a  greater  height,  to 
weigh  more,  and  to  be  more  fertile. 

A  few  other  cases  not  included  in  the  above  three 
lists  deserve  notice.  In  all  three  pots  of  Viola  tricolor, 
naturally  crossed  plants  the  offspring  of  crossed  plants 
flowered  before  naturally  crossed  plants  the  offspring 
of  self-fertilised  plants.  Flowers  on  two  plants,  both  of 
self-fertilised  parentage,  of  the  sixth  generation  of 
Mimulus  luteus  were  intercrossed,  and  other  flowers  on 
the  same  plants  were  fertilised  with  their  own  pollen ; 


Chap.  VIII.  CKOSSED    AND   SELF-FEETILISED   PLANTS.  297 

intercrossed  seedlings  and  seedlings  of  the  seventh, 
self-fertilised  generation  were  thus  raised,  and  the 
latter  flowered  before  the  intercrossed  in  three  out  of 
the  five  pots.  Flowers  on  a  plant  both  of  Mimulus 
luteus  and  of  Ipomoea  purpurea  were  crossed  with  pollen 
from  other  flowers  on  the  same  plant,  and  other  flowers 
were  fertilised  with  their  own  pollen ;  intercrossed 
seedlings  of  this  peculiar  kind,  and  others  strictly  self- 
fertilised  being  thus  raised.  In  the  case  of  the 
Mimulus  the  self-fertilised  plants  flowered  first  in  seven 
out  of  the  eight  pots,  and  in  the  case  of  the  Ipomoea 
in  eight  out  of  the  ten  pots ;  so  that  an  intercross 
between  the  flowers  on  the  same  plant  was  very  far 
from  giving  to  the  offspring  thus  raised,  any  advantage 
over  the  strictly  self-fertilised  plants  in  their  period 
of  flowering. 

Tlie  Effects  of  crossing  Flowers  on  the  same  Plant. 

In  the  discussion  on  the  results  of  a  cross  with  a  fresh 
stock,  given  under  Table  C  in  the  last  chapter,  it  was 
shown  that  the  mere  act  of  crossing  by  itself  does  no 
good  ;  but  that  the  advantages  thus  derived  depend  on 
the  plants  which  are  crossed,  either  consisting  of 
distinct  varieties  which  will  almost  certainly  differ 
somewhat  in  constitution,  or  on  the  progenitors  of  the 
plants  which  are  crossed,  though  identical  in  every 
external  character,  having  been  subjected  to  somewhat 
different  conditions  and  having  thus  acquired  some 
slight  difference  in  constitution.  All  the  flowers 
produced  by  the  same  plant  have  been  developed 
from  the  same  seed  ;  those  which  expand  at  the  same 
time  have  been  exposed  to  exactly  the  same  climatic 
influences ;  and  the  stems  have  all  been  nourished  by 
the  same  roots.  Therefore  in  accordance  with  the  con- 
clusion just  referred  to,  no  good  ought  to  result  from 


298 


THE   EFFECTS   OF   CROSSING 


Chap.  VIII. 


crossing  flowers  on  the  same  plant.*  In  opposition  to 
this  conclusion  is  the  fact  that  a  bud  is  in  one  sense 
a  distinct  individual,  and  is  capable  of  occasionally  or 
even  not  rarely  assuming  new  external  characters,  as 
well  as  new  constitutional  peculiarities.  Plants  raised 
from  buds  which  have  thus  varied  may  be  propagated 
for  a  great  length  of  time  by  grafts,  cuttings,  &c,  and 
sometimes  even  by  seminal  generation.!  There  exist 
also  numerous  species  in  which  the  flowers  on  the 
same  plant  differ  from  one  another, — as  in  the  sexual 
organs  of  monoecious  and  polygamous  plants, — in  the 
structure  of  the  circumferential  flowers  in  many  Com- 
positee,  Umbelliferae,  &c, — in  the  structure  of  the 
central  flower  in  some  plants, — in  the  two  kinds  of 
flowers  produced  by  cleistogene  species,  —  and  in 
several  other  such  cases.  These  instances  clearly 
prove  that  the  flowers  on  the  same  plant  have  often 
varied  independently  of  one  another  in  many  im- 
portant  respects,   such   variations  having  been  fixed, 


*  It  is,  however,  possible  that 
the  stamens  which  differ  in  length 
or  construction  in  the  same  flower 
may  produce  pollen  differing  in 
nature,  and  in  this  manner  a  cross 
might  be  made  effective  between 
the  several  flowers  on  the  same 
plant.  Mr.  Macnab  states  (in  a 
communication  to  M.  Verlot,  '  La 
Production  des  Variete's/  1865, 
p.  42)  that  seedlings  raised  from 
the  shorter  and  longer  stamens  of 
rhododendron  differ  in  character  ; 
but  the  shorter  stamens  appa- 
rently are  becoming  rudimentary, 
and  the  seedlings  are  dwarfs,  so 
that  the  result  may  be  simply  due 
to  a  want  of  fertilising  power  in 
the  pollen,  as  in  the  case  of  the 
dwarfed  plants  of  Mirabilis  raised 
by  Naudin  by  the  use  of  too  few 
pollen-grains.      Analogous  state- 


ments have  been  made  with  re- 
spect to  the  stamens  of  Pelargo- 
nium. With  some  of  the  Mela- 
stoinacese,  seedlings  raised  by  me 
from  flowers  fertilised  by  pollen 
from  the  shorter  stamens,  cer- 
tainly differed  in  appearance  from 
those  raised  from  the  longer  sta- 
mens, with  differently  coloured 
anthers  ;  but  here,  again,  there  is 
some  reason  for  believing  that  the 
shorter  stamens  are  tending  to- 
wards abortion.  In  the  very  dif- 
ferent case  of  trimorphic  hetero- 
styled  plants,  the  two  sets  of  sta- 
mens in  the  same  flower  have 
widely  different  fertilising  powers. 
f  I  have  given  numerous  cases 
of  such  bud- variations  in  my 'Va- 
riation of  Animals  and  Plants  un- 
der Domestication,'  chap.  xi.  2nd 
edit.  vol.  i.  p.  448. 


Chap.  VIII.       FLOWERS   ON   THE   SAME   PLANT.  299 

like  those  on  distinct  plants  during  the  develop- 
ment of  species. 

It  was  therefore  necessary  to  ascertain  by  experiment 
what  would  be  the  effect  of  intercrossing  flowers  on 
the  same  plant,  in  comparison  with  fertilising  them 
with  their  own  pollen  or  crossing  them  with  pollen 
from  a  distinct  plant.  Trials  were  carefully  made  on 
five  genera  belonging  to  four  families ;  and  in  only 
one  case,  namely,  Digitalis,  did  the  offspring  from  a 
cross  between  the  flowers  on  the  same  plant  receive 
any  benefit,  and  the  benefit  here  was  small  compared 
with  that  derived  from  a  cross  between  distinct  plants. 
In  the  chapter  on  Fertility,  when  we  consider  the 
effects  of  cross-fertilisation  and  self-fertilisation  on  the 
productiveness  of  the  parent-plants  we  shall  arrive  at 
nearly  the  same  result,  namely,  that  a  cross  between 
the  flowers  on  the  same  plant  does  not  at  all  increase 
the  number  of  the  seeds,  or  only  occasionally  and  to  a 
slight  degree.  I  will  now  give  an  abstract  of  the 
results  of  the  five  trials  which  were  made. 

(1.)  Digitalis  purpurea. — Seedlings  raised  from  inter- 
crossed flowers  on  the  same  plant,  and  others  from 
flowers  fertilised  with  their  own  pollen,  were  grown  in 
the  usual  manner  in  competition  with  one  another  on 
the  opposite  sides  of  ten  pots.  In  this  and  the  four 
following  cases,  the  details  may  be  found  under  the 
head  of  each  species.  In  eight  pots,  in  which  the 
plants  did  not  grow  much  crowded,  the  flower-stems 
on  sixteen  intercrossed  plants  were  in  height  to  those 
on  sixteen  self-fertilised  plants,  as  100  to  94.  In  the 
two  other  pots  in  which  the  plants  grew  much  crowded, 
the  flower-stems  on  nine  intercrossed  plants  were  in 
height  to  those  on  nine  self-fertilised  plants,  as  100 
to  90.  That  the  intercrossed  plants  in  these  two  latter 
pots    had  a  real   advantage   over   their  self-fertilised 


300  THE  EFFECTS   OF   CROSSING  Chap.  VIII. 

opponents,  was  well  shown  by  their  relative  weights 
when  cut  down,  which  was  as  100  to  78.  The  mean 
height  of  the  flower-stems  on  the  twenty-five  inter- 
crossed plants  in  the  ten  pots  taken  together,  was  to 
that  of  the  flower-stems  on  the  twenty-five  self-ferti- 
lised plants,  as  100  to  92.  Thus  the  intercrossed 
plants  were  certainly  superior  to  the  self-fertilised  in 
some  degree ;  but  their  superiority  was  small  compared 
with  that  of  the  offspring  from  a  cross  between  distinct 
plants  over  the  self-fertilised,  this  being  in  the  ratio 
of  100  to  70  in  height.  Nor  does  this  latter  ratio 
show  at  all  fairly  the  great  superiority  of  the  plants 
derived  from  a  cross  between  distinct  individuals  over 
the  self-fertilised,  as  the  former  produced  more  than 
twice  as  many  flower-stems  as  the  latter,  and  were 
much  less  liable  to  premature  death. 

(2.)  Ipomoea  purpurea. — Thirty-one  intercrossed  plants 
raised  from  a  cross  between  flowers  on  the  same  plants 
were  grown  in  ten  pots  in  competition  with  the  same 
number  of  self-fertilised  plants,  and  the  former  were 
to  the  latter  in  height  as  100  to  105.  So  that  the 
self-fertilised  plants  were  a  little  taller  than  the  inter- 
crossed ;  and  in  eight  out  of  the  ten  pots  a  self-fertilised 
plant  flowered  before  any  one  of  the  crossed  plants  in 
the  same  pots.  The  plants  which  were  not  greatly 
crowded  in  nine  of  the  pots  (and  these  offer  the  fairest 
standard  of  comparison)  were  cut  down  and  weighed ; 
and  the  weight  of  the  twenty-seven  intercrossed  plants 
was  to  that  of  the  twenty-seven  self-fertilised  as  100 
to  124;  so  that  by  this  test  the  superiority  of  the 
self-fertilised  was  strongly  marked.  To  this  subject  of 
the  superiority  of  the  self-fertilised  plants  in  certain 
cases,  I  shall  have  to  recur  in  a  future  chapter.  If  we 
now  turn  to  the  offspring  from  a  cross  between 
distinct   plants  when  put  into  competition  with  self- 


Chap.  VIII.     FLOWEKS   ON   THE   SAME   PLANT.  301 

fertilised  plants,  we  find  that  the  mean  height  of 
seventy -three  such  crossed  plants,  in  the  course  of  ten 
generations,  was  to  that  of  the  same  number  of 
self-fertilised  plants  as  100  to  77 ;  and  in  the  case  of 
the  plants  of  the  tenth  generation  in  weight  as  100  to 
44.  Thus  the  contrast  between  the  effects  of  crossing 
flowers  on  the  same  plant,  and  of  crossing  flowers  on 
distinct  plants,  is  wonderfully  great. 

(3.)  Mimulus  luteus. — Twenty-two  plants  raised  by 
crossing  flowers  on  the  same  plant  were  grown  in 
competition  with  the  same  number  of  self-fertilised 
plants  ;  and  the  former  were  to  the  latter  in  height  as 
100  to  105,  and  in  weight  as  100  to  103.  Moreover,  in 
seven  out  of  the  eight  pots  a  self-fertilised  plant 
flowered  before  any  of  the  intercrossed  plants.  So  that 
here  again  the  self-fertilised  exhibit  a  slight  superiority 
over  the  intercrossed  plants.  For  the  sake  of  com- 
parison, I  may  add  that  seedlings  raised  during  three 
generations  from  a  cross  between  distinct  plants  were 
to  the  self-fertilised  plants  in  height  as  100  to  65. 

(4.)  Pelargonium  zonule. — Two  plants  growing  in 
separate  pots,  which  had  been  propagated  by  cuttings 
from  the  same  plant,  and  therefore  formed  in  fact 
parts  of  the  same  individual,  were  intercrossed,  and 
other  flowers  on  one  of  these  plants  were  self-fertilised  ; 
but  the  seedlings  obtained  by  the  two  processes  did 
not  differ  in  height.  When,  on  the  other  hand,  flowers 
on  one  of  the  above  plants  were  crossed  with  pollen 
taken  from  a  distinct  seedling,  and  other  flowers  were 
self-fertilised,  the  crossed  offspring  thus  obtained  were 
to  the  self- fertilised  in  height  as  100  to  74. 

(5.)  Origanum  vulgare. — A  plant  which  had  been 
long  cultivated  in  my  kitchen  garden,  had  spread  by 
stolons  so  as  to  form  a  large  bed  or  clump.  Seedlings 
raised  by  intercrossing  flowers  on  these  plants,  which 


302  THE   EFFECTS   OF   CEOSSING  Chap.  VIII. 

strictly  consisted  of  the  same  plant,  and  other  seedlings 
raised  from  self-fertilised  flowers,  were  carefully  com- 
pared from  their  earliest  youth  to  maturity ;  and  they 
did  not  differ  at  all  in  height  or  in  constitutional 
vigour.  Some  flowers  on  these  seedlings  were  then 
crossed  with  pollen  taken  from  a  distinct  seedling,  and 
other  flowers  were  self-fertilised ;  two  fresh  lots  of 
seedlings  being  thus  raised,  which  were  the  grand- 
children of  the  plant  that  had  spread  by  stolons  and 
formed  a  large  clump  in  my  garden.  These  differed 
much  in  height,  the  crossed  plants  being  to  the 
self-fertilised  as  100  to  86.  They  differed,  also,  to  a 
wonderful  degree  in  constitutional  vigour.  The  crossed 
plants  flowered  first,  and  produced  exactly  twice  as 
many  flower-stems ;  and  they  afterwards  increased  by 
stolons  to  such  an  extent  as  almost  to  overwhelm  the 
self-fertilised  plants. 

Reviewing  these  five  cases,  we  see  that  in  four  of 
them,  the  effect  of  a  cross  between  flowers  on  the  same 
plant  (even  on  offsets  of  the  same  plant  growing  on 
separate  roots,  as  with  the  Pelargonium  and  Origa- 
num) does  not  differ  from  that  of  the  strictest  self- 
fertilisation.  Indeed,  in  two  of  the  cases  the  self-fer- 
tilised plants  were  superior  to  such  intercrossed  plants. 
With  Digitalis  a  cross  between  the  flowers  on  the  same 
plant  certainly  did  do  some  good,  yet  very  slight 
compared  with  that  from  a  cross  between  distinct 
plants.  On  the  whole  the  results  here  arrived  at,  if 
we  bear  in  mind  that  the  flower-buds  are  to  a  certain 
extent  distinct  individuals  and  occasionally  vary  inde- 
pendently of  one  another,  agree  well  with  our  general 
conclusion,  that  the  advantages  of  a  cross  depend  on 
the  progenitors  of  the  crossed  plants  possessing  some- 
what different  constitutions,  either  from  having  been 
exposed  to   different   conditions,  or   to  their  having 


Chap.  VIII.     FLOWERS   ON   THE   SAME   PLANT.  303 

varied  from  unknown  causes  in  a  manner  which  we  in 
our  ignorance  are  forced  to  speak  of  as  spontaneous. 
Hereafter  I  shall  have  to  recur  to  this  subject  of  the 
inefficiency  of  a  cross  between  the  flowers  on  the  same 
plant,  when  we  consider  the  part  which  insects  play  in 
the  cross-fertilisation  of  flowers. 

On  the  Transmission  of  the  good  Effects  from  a  Gross 
and  of  the  evil  E feds  from  Self-fertilisation. — We  have 
seen  that  seedlings  from  a  cross  between  distinct  plants 
almost  always  exceed  their  self-fertilised  opponents  in 
height,  weight,  and  constitutional  vigour,  and,  as  will 
hereafter  be  shown,  often  in  fertility.  To  ascertain 
whether  this  superiority  would  be  transmitted  beyond 
the  first  generation,  seedlings  were  raised  on  three 
occasions  from  crossed  and  self-fertilised  plants,  both 
sets  being  fertilised  in  the  same  manner,  and  therefore 
not  as  in  the  many  cases  given  in  Tables  A,  B,  and  C, 
in  which  the  crossed  plants  were  again  crossed  and  the 
self-fertilised  again  self-fertilised. 

Firstly,  seedlings  were  raised  from  self-fertilised 
seeds  produced  under  a  net  by  crossed  and  self-fer- 
tilised plants  of  Nemophila  insignis ;  and  the  latter 
were  to  the  former  in  height  as  133  to  100.  But  these 
seedlings  became  very  unhealthy  early  in  life,  and 
grew  so  unequally  that  some  of  them  in  both  lots  were 
five  times  as  tall  as  the  others.  Therefore  this  experi- 
ment was  quite  worthless ;  but  I  have  felt  bound  to 
give  it,  as  opposed  to  my  general  conclusion.  I  should 
state  that  in  this  and  the  two  following  trials,  both  sets 
of  plants  were  grown  on  the  opposite  sides  of  the  same 
pots,  and  treated  in  all  respects  alike.  The  details  of 
the  experiments  may  be  found  under  the  head  of  each 
species. 

Secondly,  a  crossed  and  a  self-fertilised  plant  of 
Heartsease  [Viola  tricolor)  grew  near  together  in  the 
14 


304  TRANSMITTED  EFFECTS   OF   A   CROSS.  Chap.  VIIL 

open  ground  and  near  to  other  plants  of  heartsease; 
and  as  both  produced  an  abundance  of  very  fine  cap- 
sules, the  flowers  on  both  were  certainly  cross-fertilised 
by  insects.  Seeds  were  collected  from  both  plants,  and 
seedlings  raised  from  them.  Those  from  the  crossed 
plants  flowered  in  all  three  pots  before  those  from  the 
self-fertilised  plants ;  and  when  fully  grown  the  former 
were  to  the  latter  in  height  as  100  to  82.  As  both  sets 
of  plants  were  the  product  of  cross-fertilisation,  the 
difference  in  their  growth  and  period  of  flowering  was 
clearly  due  to  their  parents  having  been  of  crossed  and 
self-fertilised  parentage ;  and  it  is  equally  clear  that 
they  transmitted  different  constitutional  powers  to  their 
offspring,  the  grandchildren  of  the  plants  which  were 
originally  crossed  and  self-fertilised. 

Thirdly,  the  Sweet  Pea  (Latliyrus  odoratus)  habi- 
tually fertilises  itself  in  this  country.  As  I  possessed 
plants,  the  parents  and  grandparents  of  which  had 
been  artificially  crossed  and  other  plants  descended 
from  the  same  parents  which  had  been  self-fertilised 
for  many  previous  generations,  these  two  lots  of  plants 
were  allowed  to  fertilise  themselves  under  a  net,  and 
their  self-fertilised  seeds  saved.  The  seedlings  thus 
raised  were  grown  in  competition  with  each  other  in  the 
usual  manner,  and  differed  in  their  powers  of  growth. 
Those  from  the  self-fertilised  plants  which  had  been 
crossed  during  the  two  previous  generations  were  to 
those  from  the  plants  self-fertilised  during  many  pre- 
vious generations  in  height  as  100  to  90.  These  two 
lots  of  seeds  were  likewise  tried  by  being  sown  under 
very  unfavourable  conditions  in  poor  exhausted  soil,  and 
the  plants  whose  grandparents  and  great-grandparents 
had  been  crossed  showed  in  an  unmistakable  manner 
their  superior  constitutional  vigour.  In  this  case,  as 
in  that  of  the  heartsease,  there  could  be  no  doubt  that 


Chap.  VIII.   TRANSMITTED   EFFECTS  OF    A   CROSS.  305 

the  advantage  derived  from  a  cross  between  two  plants 
was  not  confined  to  the  offspring  of  the  first  generation. 
That  constitutional  vigour  due  to  cross-parentage  is 
transmitted  for  many  generations  may  also  be  inferred 
as  highly  probable,  from  some  of  Andrew  Knight's 
varieties  of  the  common  pea,  which  were  raised  by 
crossing  distinct  varieties,  after  which  time  they  no 
doubt  fertilised  themselves  in  each  succeeding  gene- 
ration. These  varieties  lasted  for  upwards  of  sixty 
years,  "  but  their  glory  is  now  departed."  *  On  the 
other  hand,  most  of  the  varieties  of  the  common  pea, 
which  there  is  no  reason  to  suppose  owe  their  origin 
to  a  cross,  have  had  a  much  shorter  existence.  Some 
also  of  Mr.  Laxton's  varieties  produced  by  artificial 
crosses  have  retained  their  astonishing  vigour  and 
luxuriance  for  a  considerable  number  of  generations ; 
but  as  Mr.  Laxton  informs  me,  his  experience  does 
not  extend  beyond  twelve  generations,  within  which 
period  he  has  never  perceived  any  diminution  of  vigour 
in  his  plants. 

An  allied  point  may  be  here  noticed.  As  the  force 
of  inheritance  is  strong  with  plants  (of  which  abundant 
evidence  could  be  given),  it  is  almost  certain  that  seed- 
lings from  the  same  capsule  or  from  the  same  plant 
would  tend  to  inherit  nearly  the  same  constitution ;  and 
as  the  advantage  from  a  cross  depends  on  the  plants 
which  are  crossed  differing  somewhat  in  constitution, 
it  may  be  inferred  as  probable  that  under  similar  con- 
ditions a  cross  between  the  nearest  relations  would 
not  benefit  the  offspring  so  much  as  one  between  non- 
related  plants.  In  support  of  this  conclusion  we  have 
some   evidence,  as   Fritz   Miiller   has   shown   by   his 


*  See  the  evidence  on  this  head      tication,'  chap.  ix.  vol.  i.  2nd  edit. 
in   my  l  Variation  under  Domed-      p.  397. 


306  UN1FOEM  COLOITB   OF   THE   FLOWEKS   Chap.  VIIL 

valuable  experiments  on  hybrid  Abutilons,  that  the 
union  of  brothers  and  sisters,  parents  and  children, 
and  of  other  near  relations  is  highly  injurious  to  the 
fertility  of  the  offspring.  In  one  case,  moreover,  seed- 
lings from  such  near  relations  possessed  very  weak 
constitutions.*  This  same  observer  also  found  f  three 
plants  of  a  Bignonia  growing  near  together.  He  fer- 
tilised twenty-nine  flowers  on  one  of  them  with  their 
own  pollen,  and  they  did  not  set  a  single  capsule. 
Thirty  flowers  were  then  fertilised  with  pollen  from 
a  distinct  plant,  one  of  the  three  growing  together, 
and  they  yielded  only  two  capsules.  Lastly,  five 
flowers  were  fertilised  with  pollen  from  a  fourth  plant 
growing  at  a  distance,  and  all  five  produced  capsules. 
It  seems  therefore  probable,  as  Fritz  Muller  suggests, 
that  the  three  plants  growing  near  together  were 
seedlings  from  the  same  parent,  and  that  from  being 
closely  related  they  had  little  power  of  fertilising  one 
another.! 

Lastly,  the  fact  of  the  intercrossed  plants  in 
Table  A  not  exceeding  in  height  the  self-fertilised 
plants  in  a  greater  and  greater  degree  in  the  later 
generations,  is  probably  the  result  of  their  having 
become  more  and  more  closely  inter-related. 

Uniform  Colour  of  the  Floivers  on  Plants,  self-fertilised 
and  grown  under  similar  conditions  for  several  Genera- 
tions.— At  the  commencement  of  my  experiments,  the 
parent-plants  of  Mimulus  luteus,  Ijpomoea  purpurea, 
Dianthus  caryophyUus,  and  Petunia  violaeea,  raised 
from   purchased   seeds,   varied  greatly   in  the  colour 

*  'Jenaische     Zeitschrift     fur  Domestication'  (chap    xvii.   2nd 

Naturw. ;    B.  vii.,  pp.  22  and  45,  edit.  vol.  2,  p.  121)  of  hybrids  of 

1872 ;  and  1873,  pp.  441-450.  Gladiolus  and  Cistus,  any  one  of 

f  '  Bot.  Zeituni?,'  1868,  p.  626.  -which  could  be  fertilised  by  pollen 

%  Some    remarkable  cases   are  from  any  other,  but  not    by  its 

a^ven    in    my   '  Variation    under  own  pollen. 


Chap.  VIII.         ON   SELF-FEETILISED   PLANTS.  307 

of  their  flowers.  This  occurs  with  many  plants  which 
have  been  long  cultivated  as  an  ornament  for  the 
flower-garden,  and  which  have  been  propagated  by- 
seeds.  The  colour  of  the  flowers  was  a  point  to  which 
I  did  not  at  first  in  the  least  attend,  and  no  selection 
whatever  was  practised.  Nevertheless,  the  flowers 
produced  by  the  self-fertilised  plants  of  the  above 
four  species  became  absolutely  uniform  in  tint,  or  very 
nearly  so,  after  they  had  been  grown  for  some  gene- 
rations under  closely  similar  conditions.  The  inter- 
crossed plants,  which  were  more  or  less  closely 
inter-related  in  the  later  generations,  and  which  had 
been  likewise  cultivated  all  the  time  under  similar 
conditions,  became  more  uniform  in  the  colour  of 
their  flowers  than  were  the  original  parent-plants,  but 
much  less  so  than  the  self-fertilised  plants.  When 
self-fertilised  plants  of  one  of  the  later  generations 
were  crossed  with  a  fresh  stock,  and  seedlings  thus 
raised,  these  presented  a  wonderful  contrast  in  the 
diversified  tints  of  their  flowers  compared  with  those  of 
the  self-fertilised  seedlings.  As  such  cases  of  flowers 
becoming  uniformly  coloured  without  any  aid  from 
selection  seem  to  me  curious,  I  will  give  a  full 
abstract  of  my  observations. 

Mimulus  luteus. — A  tall  variety,  bearing  large,  almost 
white  flowers  blotched  with  crimson,  appeared  amongst 
the  intercrossed  and  self-fertilised  plants  of  the  third 
and  fourth  generations.  This  variety  increased  so 
rapidly,  that  in  the  sixth  generation  of  self-fertilised 
plants  every  single  one  consisted  of  it.  So  it  was 
with  all  the  many  plants  which  were  raised,  up  to  the 
last  or  ninth  self-fertilised  generation.  Although  this 
variety  first  appeared  amongst  the  intercrossed  plants, 
yet  from  their  offspring  being  intercrossed  in  each 
succeeding   generation,  it  never  prevailed    amongst 


308  UNIFORM  COLOUR  OF   THE   FLOWERS   Chap.  VII L 

them;  and  the  flowers  on  the  several  intercrossed 
plants  of  the  ninth  generation  differed  considerably  in 
colour.  On  the  other  hand,  the  uniformity  in  colour 
of  the  flowers  on  the  plants  of  all  the  later  self-fer- 
tilised generations  was  quite  surprising ;  on  a  casual 
inspection  they  might  have  been  said  to  be  quite  alike, 
but  the  crimson  blotches  were  not  of  exactly  the  same 
shape,  or  in  exactly  the  same  position.  Both  my 
gardener  and  myself  believe  that  this  variety  did 
not  appear  amongst  the  parent-plants,  raised  from  pur- 
chased seeds,  but  from  its  appearance  amongst  both  the 
crossed  and  self-fertilised  plants  of  the  third  and  fourth 
generations ;  and  from  what  I  have  seen  of  the  variation 
of  this  species  on  other  occasions,  it  is  probable  that  it 
would  occasionally  appear  under  any  circumstances. 
We  learn,  however,  from  the  present  case  that  under 
the  peculiar  conditions  to  which  my  plants  were 
subjected,  this  particular  variety,  remarkable  for  its 
colouring,  largeness  of  the  corolla,  and  increased 
height  of  the  whole  plant,  prevailed  in  the  sixth  and 
all  the  succeeding  self-fertilised  generations  to  the 
complete  exclusion  of  every  other  variety. 

Ipomoea  purpurea. — My  attention  was  first  drawn  to 
the  present  subject  by  observing  that  the  flowers  on  all 
the  plants  of  the  seventh  self-fertilised  generation  were 
of  a  uniform,  remarkably  rich,  dark  purple  tint.  The 
many  plants  which  were  raised  during  the  three  suc- 
ceeding generations,  up  to  the  last  or  tenth,  all  produced 
flowers  coloured  in  the  same  manner.  They  were 
absolutely  uniform  in  tint,  like  those  of  a  constant 
species  living  in  a  state  of  nature ;  and  the  self-fertilised 
plants  might  have  been  distinguished  with  certainty, 
as  my  gardener  remarked,  without  the  aid  of  labels, 
from  the  intercrossed  plants  of  the  later  generations. 
These,  however,  had  more  uniformly  coloured  flowers 


Chap.  VIII.         ON   SELF-FERTILISED   PLANTS.  309 

than  those  which  were  first  raised  from  the  purchased 
seeds.  This  dark  purple  variety  did  not  appear,  as 
far  as  my  gardener  and  myself  could  recollect,  before 
the  fifth  or  sixth  self-fertilised  generation.  However 
this  may  have  been,  it  became,  through  continued 
self-fertilisation  and  the  cultivation  of  the  plants 
under  uniform  conditions,  perfectly  constant,  to  the 
exclusion  of  every  other  variety. 

JDianthus  caryophyllus. — The  self-fertilised  plants  of 
the  third  generation  all  bore  flowers  of  exactly  the 
same  pale  rose-colour ;  and  in  this  respect  they  differed 
quite  remarkably  from  the  plants  growing  in  a  large 
bed  close  by  and  raised  from  seeds  purchased  from  the 
same  nursery  garden.  In  this  case  it  is  not  improbable 
that  some  of  the  parent-plants  which  were  first  self- 
fertilised  may  have  borne  flowers  thus  coloured ;  but 
as  several  plants  were  self-fertilised  in  the  first  genera- 
tion, it  is  extremely  improbable  that  all  bore  flowers 
of  exactly  the  same  tint  as  those  of  the  self-fertilised 
plants  of  the  third  generation.  The  intercrossed  plants 
of  the  third  generation  likewise  produced  flowers 
almost,  though  not  quite  so  uniform  in  tint  as  those 
of  the  self-fertilised  plants. 

Petunia  violacea. — In  this  case  I  happened  to  record 
in  my  notes  that  the  flowers  on  the  parent-plant  which 
was  first  self- fertilised  were  of  a  "  dingy  purple  colour." 
In  the  fifth  self-fertilised  generation,  every  one  of  the 
twenty-one  self-fertilised  plants  growing  in  pots,  and 
all  the  many  plants  in  a  long  row  out  of  doors, 
produced  flowers  of  absolutely  the  same  tint,  namely, 
of  a  dull,  rather  peculiar  and  ugly  flesh  colour ;  there- 
fore, considerably  unlike  those  on  the  parent-plant.  I 
believe  that  this  change  of  colour  supervened  quite 
gradually ;  but  I  kept  no  record,  as  the  point  did  not 
interest  me  until  I  was  struck  with  the  uniform  tiut 


310  UNIFORM   COLOUR   OF   THE   FLOWEES   Chap.  VIII. 

of  the  flowers  on  the  self-fertilised  plants  of  the  fifth 
generation.  The  flowers  on  the  intercrossed  plants  of 
the  corresponding  generation  were  mostly  of  the  same 
dull  flesh  colour,  but  not  nearly  so  uniform  as  those  on 
the  self-fertilised  plants,  some  few  being  very  pale, 
almost  white.  The  self-fertilised  plants  which  grew  in 
a  long  row  in  the  open  ground  were  also  remarkable  for 
their  uniformity  in  height,  as  were  the  intercrossed 
plants  in  a  less  degree,  both  lots  being  compared  with 
a  large  number  of  plants  raised  at  the  same  time  under 
similar  conditions  from  the  self-fertilised  plants  of  the 
fourth  generation  crossed  by  a  fresh  stock.  I  regret 
that  I  did  not  attend  to  the  uniformity  in  height  of 
the  self-fertilised  seedlings  in  the  later  generations  of 
the  other  species. 

These  few  cases  seem  to  me  to  possess  much  interest. 
We  learn  from  them  that  new  and  slight  shades  of 
colour  may  be  quickly  and  firmly  fixed,  independently 
of  any  selection,  if  the  conditions  are  kept  as  nearly 
uniform  as  is  possible,  and  no  intercrossing  be  per- 
mitted. With  Mimulus,  not  only  a  grotesque  style  of 
colouring,  but  a  larger  corolla  and  increased  height  of 
the  whole  plant  were  thus  fixed ;  whereas  with  most 
plants  which  have  been  long  cultivated  for  the  flower- 
garden,  no  character  is  more  variable  than  that  of 
colour,  excepting  perhaps  that  of  height.  From  the 
consideration  of  these  cases  we  may  infer  that  the 
variability  of  cultivated  plants  in  the  above  respects 
is  due,  firstly,  to  their  being  subjected  to  somewhat 
diversified  conditions,  and,  secondly,  to  their  being 
often  inter-crossed,  as  would  follow  from  the  free  access 
of  insects.  I  do  not  see  how  this  inference  can  be 
avoided,  as  when  the  above  plants  were  cultivated 
for  several  generations  under  closely  similar  conditions, 
and  were  intercrossed  in  each  generation,  the  colour 


Chap.  VIII.        ON   SELF-FERTILISED   PLANTS.  311 

of  their  flowers  tended  in  some  degree  to  change  and  to 
become  uniform.  When  no  intercrossing  with  other 
plants  of  the  same  stock  was  allowed, — that  is,  when 
the  flowers  were  fertilised  with  their  own  pollen  in 
each  generation — their  colour  in  the  later  generations 
became  as  uniform  as  that  of  plants  growing  in  a 
state  of  nature,  accompanied  at  least  in  one  instance 
by  much  uniformity  in  the  height  of  the  plants.  But 
in  saying  that  the  diversified  tints  of  the  flowers  on 
cultivated  plants  treated  in  the  ordinary  manner  are 
due  to  differences  in  the  soil,  climate,  &c,  to  which 
they  are  exposed,  I  do  not  wish  to  imply  that  such 
variations  are  caused  by  these  agencies  in  any  more 
direct  manner  than  that  in  which  the  most  diversified 
illnesses,  as  colds,  inflammation  of  the  lungs  or  pleura, 
rheumatism,  &c,  may  be  said  to  be  caused  by  expo- 
sure to  cold.  In  both  cases  the  constitution  of  the 
being  which  is  acted  on  is  of  preponderant  importance. 


312  FERTILITY   OF   CEOSSED  Chap.  IX. 


CHAPTEE  IX. 

The  Effects  of  Cross-fertilisation  and  Self-fertilisation  on 
the  Production  of  Seeds. 

Fertility  of  plants  of  crossed  and  self-fertilised  parentage,  both  lots 
being  fertilised  in  the  same  manner — Fertility  of  the  parent-plants 
when  first  crossed  and  self-fertilised,  and  of  their  crossed  and  self- 
fertilised  offspring  when  again  crossed  and  self-fertilised — Com- 
parison of  the  fertility  of  flowers  fertilised  with  their  own  pollen 
and  with  that  from  other  flowers  on  the  same  plant — Self-sterile 
plants — Causes  of  self-sterility — The  appearance  of  highly  self- 
fertile  varieties — Self-fertilisation  apparently  in  some  respects  bene- 
ficial, independently  of  the  assured  production  of  seeds. — Relative 
weights  and  rates  of  germiuation  of  seeds  from  crossed  and  t-.elf- 
fertilised  flowers. 

The  present  chapter  is  devoted  to  the  Fertility  of 
plants,  as  influenced  by  cross-fertilisation  and  self- 
fertilisation.  The  subject  consists  of  two  distinct 
branches ;  firstly,  the  relative  productiveness  or  fertility 
of  flowers  crossed  with  pollen  from  a  distinct  plant  and 
with  their  own  pollen,  as  shown  by  the  proportional 
number  of  capsules  which  they  produce,  together 
with  the  number  of  the  contained  seeds.  Secondly, 
the  degree  of  innate  fertility  or  sterility  of  the  seed- 
lings raised  from  crossed  and  self-fertilised  seeds ;  such 
seedlings  being  of  the  same  age,  grown  under  the  same 
conditions,  and  fertilised  in  the  same  manner.  These 
two  branches  of  the  subject  correspond  with  the  two 
which  have  to  be  considered  by  any  one  treating  of 
hybrid  plants;  namely,  in  the  first  place  the  comparative 
productiveness  of  a  species  when  fertilised  with  pollen 
from  a  distinct  species  and  with  its  own  pollen ;  and 


Chap.  IX.         AND   SELF-FEKTILISED  PLANTS.  313 

in  the  second  place,  the  fertility  of  its  hybrid  off- 
spring. These  two  classes  of  cases  do  not  always  run 
parallel ;  thus  some  plants,  as  Gartner  has  shown,  can 
be  crossed  with  great  ease,  but  yield  excessively  sterile 
hybrids ;  while  others  are  crossed  with  extreme  diffi- 
culty, but  yield  fairly  fertile  hybrids. 

The  natural  order  to  follow  in  this  chapter  would 
have  been  first  to  consider  the  effects  on  the  fertility 
of  the  parent-plants  of  crossing  them,  and  of  fertilising 
them  with  their  own  pollen  ;  but  as  we  have  discussed 
in  the  two  last  chapters  the  relative  height,  weight, 
and  constitutional  vigour  of  crossed  and  self-fertilised 
plants — that  is,  of  plants  raised  from  crossed  and 
self-fertilised  seeds — it  will  be  convenient  here  first 
to  consider  their  relative  fertility.  The  cases  observed 
by  me  are  given  in  the  following  table,  D,  in  which 
plants  of  crossed  and  self-fertilised  parentage  were  left 
to  fertilise  themselves,  being  either  crossed  by  insects 
or  spontaneously  self-fertilised.  It  should  be  observed 
that  the  results  cannot  be  considered  as  fully  trust- 
worthy, for  the  fertility  of  a  plant  is  a  most  variable 
element,  depending  on  its  age,  health,  nature  of  the 
soil,  amount  of  water  given,  and  temperature  to  which 
it  is  exposed.  The  number  of  the  capsules  produced 
and  the  number  of  the  contained  seeds,  ought  to  have 
been  ascertained  on  a  large  number  of  crossed  and  self- 
fertilised  plants  of  the  same  age  and  treated  in  every 
respect  alike.  In  these  two  latter  respects  my  observa- 
tions may  be  trusted,  but  a  sufficient  number  of  capsules 
were  counted  only  in  a  few  instances.  The  fertility, 
or  as  it  may  perhaps  better  be  called  the  productive- 
ness, of  a  plant  depends  on  the  number  of  capsules 
produced,  and  on  the  number  of  seeds  which  these 
contain.  But  from  various  causes,  chiefly  from  the 
want  of  time,  I  was  often  compelled  to  rely  on  the 


314 


FERTILITY  OF   CROSSED 


Chap.  IX. 


number  of  the  capsules  alone.  Nevertheless,  in  the 
more  interesting  cases,  the  seeds  were  also  counted 
or  weighed.  The  average  number  of  seeds  per  capsule 
is  a  more  valuable  criterion  of  fertility  than  the 
number  of  capsules  produced.  This  latter  circum- 
stance depends  partly  on  the  size  of  the  plant ;  and  we 
know  that  crossed  plants  are  generally  taller  and 
heavier  than  the  self- fertilised ;  but  the  difference  in 
this  respect  is  rarely  sufficient  to  account  for  the 
difference  in  the  number  of  the  capsules  produced.  It 
need  hardly  be  added  that  in  the  following  table  the 
same  number  of  crossed  and  self-fertilised  plants  are 
always  compared.  Subject  to  the  foregoing  sources  of 
doubt  I  will  now  give  the  table,  in  which  the  parentage 
of  the  plants  experimented  on,  and  the  manner  of 
determining  their  fertility  are  explained.  Fuller 
details  may  be  found  in  the  previous  part  of  this  work, 
under  the  head  of  each  species. 

Table  D. — ■Relative  Fertility  of  Plants  of  crossed  and  self -fertilised 
Parentage,  both  sets  being  fertilised  in  the  same  manner.  Fer- 
tility judged  of  by  various  Standards.  That  of  the  crossed  Plants 
taken  as  100. 


Ipomcea    purpurea — first  generation:    seeds    per  capsule] 

on  crossed  and  self-fertilised   plants,  not  growing  much)!      .„  ,      ^q 
crowded,    spontaneously  self-fertilised    under    a   net,    inf 
number J 

Ipomcea  purpurea — seeds  per  capsule  on  crossed  and] 
self-fertilised  plants  from  the  same  parents  as  in  the  last  I 
case,  but  growing  much  crowded,  spontaneously  self- 1 
fertilised  under  a  net,  in  number J 

Ipomcea  purpurea — productiveness  of  the  same  plants,  asl 
judged  by  the  number  of  capsules  produced,  and  average  \ 
number  of  seeds  per  capsule ) 

Ipomcea  purpurea — third  generation:  seeds  per  capsule) 
on  crossed  and  self- fertilised  plants,  spontaneously  self-> 
fertilised  under  a  net,  in  number j 

Iiomcea  purpurea — productiveness  of  the  same  plants,! 
as  judged  by  number  of  capsules  produced,  and  averaged 
number  of  seeds  per  capsule ) 


93 

45 
94 
35 


Chvp  IX.  AND   SELF-FEKTILISED   PLANTS. 

Table  D — continued. 


315 


IPOMCEA  purpurea — fifth  generation :  seeds  per  capsule 
on  crossed  and  self-fertilised  plants,  left  uncovered  in  the 
hothouse,  and  spontaneously  fertilised 

Ipomcea  purpurea — ninth  generation  :  number  of  capsules 
on  crossed  plants  to  those  on  self-fertilised  plants,  spon- 
taneously self-fertilised  under  a  net 

Mimulus  luteus — an  equal  number  of  capsules  on  plants' 
descended  from  self-fertilised  plants  of  the  8th  genera- 
tion crossed  by  a  fresh  stock,  and  on  plants  of  the  9th 
self-fertilised  generation,  both  sets  having  been  left 
uncovered  and  spontaneously  fertilised,  contained  seeds, 
by  weight 

Mimulus  luteus — productiveness  of  the  same  plants,  as 
judged  by  number  of  capsules  produced,  and  average 
weight  of  seeds  per  capsule 

Vanoellia  nummularifolia — seeds  per  capsule  from) 
cleistogene  flowers  on  the  crossed  and  self-fertilised) 
plants,  in  number .      .) 

Salvia  COCCiNEA — crossed  plants,  compared  with  self-fer- 
tilised plants,  produced  flowers,  in  number      .... 

Iberis  umbellata — plants  left  uncovered  in  greenhouse ; 
intercrossed  plants  of  the  3rd  generation,  compared  with 
self-fertilised  plants  of  the  3rd  generation,  yielded  sepds, 
in  number 

Iberis  umbellata — plants  from  a  cross  between  two] 
varieties,  compared  with  self- fertilised  plants  of  the  3rd> 
generation,  yielded  seeds,  by  weight J 

Papaver  VAGUM — crossed  and  self-fertilised  plants,  left 
uncovered,  produced  capsules,  in  number 

Eschscholtzia  CALIFORNICA — Brazilian  stock ;  plants  left 
uncovered  and  cross-fertilised  by  bees ;  capsules  on 
intercrossed  plants  of  2nd  generation,  compared  with 
capsules  on  self-fertilised  plants  of  2nd  generation,  con- 
tained seeds,  in  number 

Eschscholtzia  californica — productiveness  of  the  same) 
plants,  as  judged  by  number  of  capsules  produced,  and> 
average  number  of  seeds  per  capsule J 

Eschscholtzia  californica — plants  left  uncovered  and' 
cross-fertilised  by  bees :  capsules  on  plants  derived  from 
intercrossed  plants  of  2nd  generation  of  the  Brazilian 
ttock  crossed  by  English  stock,  compared  with  capsules 
on  self-fertilised  plants  of  2nd  generation,  contained 
seeds,  in  number 


Eschscholtzia  californica — productiveness  of  the  same) 
plants,  as  judged  by  number  of  capsules  produced,  and> 
average  number  of  seeds  per  capsule J 


as  100  to    89 


26 


30 


106 
57 

75 

75 
99 

78 
89 

63 

.40 


316 


FERTILITY    OF   CROSSED 
Table  D — continued. 


Chap.  IX. 


Reseda  Odorata — crossed  and  self-fertilised  plants,  left 
uncovered  and  cress-fertilised  by  bees,  produced  capsules 
in  number  (about) 

Viola  tricolor — crossed  and  s_elf-fertilised  plants,  left 
uncovered  and  cross-fertilised  by  bees,  produced  capsules 
in  number 

Delphinium  CONSOLIDA — crossed  and  self-fertilised  plants, 
left  uncovered  in  the  greenhouse,  produced  capsules  in 
number 

Viscaria  oculata — crossed  and  self-fertilised  plants,  left 
uncovered  in  the  greenhouse,  produced  capsules  in  number 

DlANTHUS  CARYOPHYLLUS — plants  spontaneously  self-ferti- 
lised under  a  net ;  capsules  on  intercrossed  and  self- 
fertilised  plants  of  the  3rd  generation  contained  seeds  in 
number 

Dianthus  caryophyllus — plants  left  uncovered  and  cross-1 
fertilised  by  insects :  offspring  from  plants  self-fertilised 
for  three  generations  and  then  crossed  by  an  inter- 
crossed plant  of  the  same  stock,  compared  with  plants 
of  the  4th  self-fertilised  generation,  produced  seeds  by 
weight 

Dianthus  caryophyllus — plants  left  uncovered  and  cross- 
fertilised  by  insects  :  offspring  from  plants  self-fertilised 
for  three  generations  and  then  crossed  by  a  fresh 
stock,  compared  with  plants  of  the  4th  self-fertilised 
generation,  produced  seeds  by  weight 

Trop^eolum  minus — crossed  and  self-fertilised  plants,  Ieft\ 
uncovered  in  the  greenhouse,  produced  seeds  in  number  ./ 

Limnanthes  douglasii — crossed  and  self-fertilised  plants, 
left  uncovered  in  greenhouse,  produced  capsules  in 
number  (about) 

Lupinus  luteus — crossed  and  self-fertilised  plants  of  the 
2nd  generation,  left  uncovered  in  the  greenhouse,  pro- 
duced seeds  in  number  (judged  from  only  a  few  pods) 

Phaseolus  multiflorus — crossed  and  self-fertilised  plants, 
left  uncovered  in  the  greenhouse,  produced  seeds  in 
number  (about) 

Lathyrus  ODORATUS — crossed  and  self-fertilised  p?an'.s  wf 
the  2nd  generation,  left  uncovered  in  the  greenhouse,  but 
certainly  self-fertilised,  produced  pods  in  number 

Clarkia  ele&ANS — crossed  and  self-fertilised  plants,  left"! 
uncovered  in  the  greenhouse,  produced  capsules  in  number/ 

Nemophila  insignis — crossed  and  self-fertilised  plants,! 
covered  by  a  net  and  spontaneously  self-fertilised  in  the> 
greenhouse,  produced  capsules  in  number ) 

rETUNiA  VIOLacea — left  uncovered  and  cross- fertilised  by] 
insects  :  plants  of  the  5th  intercrossed  and  self-fertilised  I 
generations  produced  seeds,  as  judged  by  the  weight  of  an  | 
equal  number  of  capsules J 


as  100  to  100 


10 


„  56 
„  77 
„  125 

»  73 
„     33 


>, 

„     64 

)) 

„  100 

,, 

„     88 

» 

„ioo 

»» 

„    91 

29 


;,        86 


Chap.  IX.  AND   SELF-FEKTTLISED  PLANTS. 

Table  D — continued. 


317 


Petunia  viol  ace  A — left  uncovered  as  above:  offspring  of 
plants  self- fertilised  for  four  generations  and  then  crossed 
by  a  fresh  stock,  compared  with  plants  of  the  5th  self- 
fertilised  generation,  produced  seeds,  as  judged  by  the 
weight  of  an  equal  number  of  capsules 

Cyclamen  persicum — crossed  and  self-fertilised  plants,  left \ 
uncovered  in  the  greenhouse,  produced  capsules  in  number/ 

Anagallis  COLLINA  — crossed  and  self-fertilised  plants,  left"! 
uncovered  in  the  greenhouse,  produced  capsules  in  number/ 

Primula  veris — left  uncovered  in  open  ground  and  cross-') 
fertilised  by  insects:  offspring  from  plants  of  the  3rd] 
illegitimate  generation  crossed  by  a  fresh  stock,  compared  > 
with    plants  of  the  4th  illegitimate    and  self-fertilised 

generation,  produced  capsules  in  number J 

Same  plants  in  the  following  year 

Primula  veris — (equal-styled  variety):  left  uncovered  in) 
open  ground    and   cross-fertilised   by   insects:    offspring | 
from  plants  self-fertilised  for  two  generations  and  then}- 
crossed  by  another  variety,  compared  with  plants  of  the  3rd 
self-fertilised  generation,  produced  capsules  in  number 

Primula  veris — (equal-styled  var.)  same  plants  ;  average 
number  of  seeds  per  capsule 

Primula  veris — (equal-styled  var.)  productiveness  of  the  1 
same  plants,  as  judged  by  number  of  capsules  produced) 
and  average  number  of  seeds  per  capsule ) 


as  100  to    46 


12 
8 


,       „     71 


This  table  includes  thirty-three  cases  relating  to 
twenty-three  species,  and  shows  the  degree  of  innate 
fertility  of  plants  of  crossed  parentage  in  comparison 
with  those  of  self-fertilised  parentage  ;  both  lots  being 
fertilised  in  the  same  manner.  With  several  of  the 
species,  as  with  Eschscholtzia,  Reseda,  Yiola,  Dian- 
thus,  Petunia,  and  Primula,  both  lots  were  certainly 
cross-fertilised  by  insects,  and  so  it  probably  was  with 
several  of  the  others ;  but  in  some  of  the  species,  as 
with  Nemophila,  and  in  some  of  the  trials  with  Ipomoea 
and  Dianthus,  the  plants  were  covered  up,  and  both 
Jots  were  spontaneously  self-fertilised.  This  also  was 
necessarily  the  case  with  the  capsules  produced  by  the 
cleistogene  flowers  of  Yandellia. 


318  FEETILITY  OP   CEOSSED  Chap.  IX. 

The  fertility  of  the  crossed  plants  is  represented  in 
the  table  by  100,  and  that  of  the  self-fertilised  by  the 
other  figures.  There  are  five  cases  in  which  the  fertility 
of  the  self-fertilised  plants  is  approximately  equal  to 
that  of  the  crossed  ;  nevertheless,  in  four  of  these  cases 
the  crossed  plants  were  plainly  taller,  and  in  the  fifth 
somewhat  taller  than  the  self-fertilised.  But  I  should 
state  that  in  some  of  these  five  cases  the  fertility  of 
the  two  lots  was  not  strictly  ascertained,  as  the  capsules 
were  not  actually  counted,  from  appearing  equal  in 
number  and  from  all  apparently  containing  a  full  com- 
plement of  seeds.  In  only  two  instances  in  the  table, 
viz.,  with  Vandellia  and  in  the  third  generation  of 
Dianthus,  the  capsules  on  the  self-fertilised  plants 
contained  more  seed  than  those  on  the  crossed  plants. 
With  Dianthus  the  ratio  between  the  number  of  seeds 
contained  in  the  self-fertilised  and  crossed  capsules 
was  as  125  to  100 ;  both  sets  of  plants  were  left  to 
fertilise  themselves  under  a  net;  and  it  is  almost 
certain  that  the  greater  fertility  of  the  self-fertilised 
plants  was  here  due  merely  to  their  having  varied 
and  become  less  strictly  dichogamous,  so  as  to  mature 
their  anthers  and  stigmas  more  nearly  at  the  same 
time  than  is  proper  to  the  species.  Excluding  the 
seven  cases  now  referred  to,  there  remain  twenty-six 
in  which  the  crossed  plants  were  manifestly  much 
more  fertile,  sometimes  to  an  extraordinary  degree, 
than  the  self-fertilised  with  which  they  grew  in  com- 
petition. The  most  striking  instances  are  those  in 
which  plants  derived  from  a  cross  with  a  fresh  stock 
are  compared  with  plants  of  one  of  the  later  self-fer- 
tilised generations ;  yet  there  are  some  striking  cases, 
as  that  of  Viola,  between  the  intercrossed  plants  of  the 
same  stock  and  the  self-fertilised,  even  in  the  first 
generation.     The  results  most  to  be  trusted  are  those 


Chap.  IX. 


AND    SELF-FEKTTLISED    PLANTS. 


319 


in  which  the  productiveness  of  the  plants  was  ascei> 
tained  by  the  number  of  capsules  produced  by  an 
equal  number  of  plants,  together  with  the  actual  or 
average  number  of  seeds  in  each  capsule.  Of  such 
cases  there  are  twelve  in  the  table,  and  the  mean  of 
their  mean  fertility  is  as  100  for  the  crossed  plants, 
to  59  for  the  self-fertilised  plants.  The  Primulaceae 
seem  eminently  liable  to  suffer  in  fertility  from  self- 
fertilisation. 

The  following  short  table,  E,  includes   four   cases 
which  have  already  been  partly  given  in  the  last  table. 


Table  E. — Innate  Fertility  of  Plants  from  a  Cross  ivith  a  fresh 
Stock,  compared  vriih  that  of  Intercrossed  Plants  of  the  same 
Stock,  and  with  that  of  Self -fertilised  Plants,  all  of  the  corre~ 
sponding  Generation.  Fertility  judged  of  by  the  number  or 
weight  of  seeds  produced  by  an  equal  number  of  Plants. 


Plants  from  a 
Cross  with  a 
Fresh  Stock. 

Intercrossed 
Plants  of  the 
same  Stock. 

•a 

Mimulus  luteus — the  intercrossed  plants  are  de-1 
rived  from  a  cross  between  two  plants  of  the  | 
8th  self-fertilised  generation.    The  self-fertilised 
plants  belong  to  the  9th  generation  .      .      .      .J 

Eschscholtzia  californica — the  intercrossed  and\ 
self-fertilised  plants  belong  to  the  2nd  generation) 

DiANTHUSCiRTOPHYLLUS — the  intercrossed  plants' 
are  derived  from   self-fertilised  of  the  3rd  ge- 
neration, crossed  by  intercrossed  plants    of  the> 
3rd  generation.    The  self-fertilised  plants  belong 

Petunia  VIOLACEA — the  intercrossed  and  self-fer-"! 
til  ised  plants  belong  to  the  5th  generation    .      .  J 

100 
100 

100 

100 

4 
45 

45 

54 

3 
40 

33 

46 

N.B. — In  the  above  cases,  excepting  in  that  of  Eschscholtzia,  the  plants 
derived  from  a  cross  with  a  fresh  stock  belong  on  the  mother-side  to  the 
same  stock  with  the  intercrossed  and  self-fertilised  plants,  and  to  the  cor- 
responding generation. 


320  FERTILITY   OF   CEOSSED  Chap.  IX. 

These  cases  show  us  how  greatly  superior  in  innate 
fertility  the  seedlings  from  plants  self-fertilised  or 
intercrossed  for  several  generations  and  then  crossed 
by  a  fresh  stock  are,  in  comparison  with  the  seedlings 
from  plants  of  the  old  stock,  either  intercrossed  or 
self-fertilised  for  the  same  number  of  generations.  The 
three  lots  of  plants  in  each  case  were  left  freely  ex- 
posed to  the  visits  of  insects,  and  their  flowers  without 
doubt  were  cross-fertilised  by  them. 

This  table  further  shows  us  that  in  all  four  cases  the 
intercrossed  plants  of  the  same  stock  still  have  a 
decided  though  small  advantage  in  fertility  over  the 
self-fertilised  plants. 

With  respect  to  the  state  of  the  reproductive  organs 
in  the  self-fertilised  plants  of  the  two  last  tables, 
only  a  few  observations  were  made.  In  the  seventh 
and  eighth  generation  of  Iponioea,  the  anthers  in  the 
flowers  of  the  self-fertilised  plants  were  plainly  smaller 
than  those  in  the  flowers  of  t-he  intercrossed  plants. 
The  tendency  to  sterility  in  these  same  plants  was 
also  shown  by  the  first-formed  flowers,  after  they  had 
been  carefully  fertilised,  often  dropping  off,  in  the 
same  manner  as  frequently  occurs  with  hybrids.  The 
flowers  likewise  tended  to  be  monstrous.  In  the 
fourth  generation  of  Petunia,  the  pollen  produced 
by  the  self-fertilised  and  intercrossed  plants  was 
compared,  and  there  were  far  more  empty  and  shrivelled 
grains  in  the  former. 

Relative  Fertility  of  Flowers  crossed  with  Pollen  from  a 
distinct  Plant  and  with  their  own  Pollen.  This  heading 
includes  flowers  on  the  Parent-plants,  and  on  the  crossed 
and  self-fertilised  Seedlings  of  the  first  or  a  succeeding  Ge- 
neration.— I  will  first  treat  of  the  parent-plants,  which 


Chap.  IX.        AND   SELF-FERTILISED  FLOWERS.  321 

were  raised  from  seeds  purchased  from  nursery-gardens, 
or  taken  from  plants  growing  in  my  garden,  or 
growing  wild,  and  surrounded  in  every  case  by  many 
individuals  of  the  same  species.  Plants  thus  circum- 
stanced will  commonly  have  been  intercrossed  by 
insects ;  so  that  the  seedlings  which  were  first  ex- 
perimented on  will  generally  have  been  the  product 
of  a  cross.  Consequently  any  difference  in  the 
fertility  of  their  flowers,  when  crossed  and  self-fer- 
tilised, will  have  been  caused  by  the  nature  of  the 
pollen  employed ;  that  is,  whether  it  was  taken  from 
a  distinct  plant  or  from  the  same  flower.  The  de- 
grees of  fertility  shown  in  the  following  table,  F, 
were  determined  in  each  case  by  the  average  number 
of  seeds  per  capsule,  ascertained  either  by  counting 
or  weighing. 

Another  element  ought  properly  to  have  been  taken 
into  account,  namely,  the  proportion  of  flowers  which 
yielded  capsules  when  they  were  crossed  and  self-fer- 
tilised; and  as  crossed  flowers  generally  produce  a 
larger  proportion  of  capsules,  their  superiority  in  fer- 
tility, if  this  element  had  been  taken  into  account, 
would  have  been  much  more  strongly  marked  than 
appears  in  Table  F.  But  had  I  thus  acted,  there 
would  have  been  greater  liability  to  error,  as  pollen 
applied  to  the  stigma  at  the  wrong  time  fails  to  pro- 
duce any  effect,  independently  of  its  greater  or  less 
potency.  A  good  illustration  of  the  great  difference 
in  the  results  which  sometimes  follows,  if  the  number 
of  capsules  produced  relatively  to  the  number  of  flowers 
fertilised  be  included  in  the  calculation,  was  afforded 
by  Nolana  prostrata.  Thirty  flowers  on  some  plants 
of  this  species  were  crossed  and  produced  twenty-seven 
capsules,  each  containing  five  seeds ;  thirty-two  flowers 
on  the  same  plants  were  self-fertilised  and  produced 


322 


FERTILITY   OF   CROSSED 


Chap.  IX. 


only  six  capsules,  each  containing  five  seeds.  As  the 
number  of  seeds  per  capsule  is  here  the  same,  the  fer- 
tility of  the  crossed  and  self-fertilised  flowers  is  given 
in  Table  F  as  equal,  or  as  100  to  100.  But  if  the 
flowers  which  failed  to  produce  capsules  be  included, 
the  crossed  flowers  yielded  on  an  average  4 '  50  seeds, 
whilst  the  self-fertilised  flowers  yielded  only  0 '  91  seeds, 
so  that  their  relative  fertility  would  have  been  as  100 
to  21.  I  should  here  state  that  it  has  been  found  con- 
venient to  reserve  for  separate  discussion  the  cases  of 
flowers  which  are  usually  quite  sterile  with  their  own 
pollen. 


Table  F. — Relative  Fertility  of  the  Flowers  on  the  Parent-plants 
used  in  my  Experiments,  when  fertilised  with  Pollen  from  a, 
distinct  Plant  and  with  their  own  Pollen.  Fertility  judged  of 
hy  the  average  Number  of  Seeds  per  Capsule.  Fertility  of 
Crossed  Flowers  taken  as  100. 


Iposicea  purpurea — crossed  and  self-fertilised  flowers'! 
yielded  seeds  as  (about) .  j 

Miliums  LUTEUS — crossed  and  self-fertilised  flowers  yielded"! 

seeds  as  (by  weight) J 

Lijtaria    vulgaris  —  crossed    and    self-fertilised    flowers') 

yielded  seeds  as / 

Vandellia    nummularifolia — crossed  and   self-fertilised  \ 

flowers  yielded  seeds  as / 

Gesneria   fendulina — crossed  and  self-fertilised  flowers'! 

yielded  seeds  as  (by  weight) J 

Salvia  COCCInea — crossed  and  self- fertilised  flowers  yielded} 

seeds  as  (about) j 

Brassica  OLERACEA  —  crossed  and  self-fertilised  flowers'! 
yielded  seeds  as J 

ESCHSCHOLTZIA  californica — (English  stock)  crossed  andj 
self-fertilised  flowers  yielded  seeds  as  (by  weight)       .      ./ 

ESCHSCHOLTZIA  CALiFORNiOA — (Brazilian  stock  grown  in) 
England)  crossed  and  self-fertilised  flowers  yielded  seeds  [ 
(by  weight)  as  (about) j 

Delphinium  consolida — crossed  and  self-fertilised  flowers) 
(self-fertilised  capsules  spontaneously  produced,  but  result  > 
supported  by  other  evidence)  yielded  seeds  as  .      .      .      .  j 


100 


to 

100 

» 

79 

H 

14 

)) 

67? 

;j 

100 

5! 

100 

;> 

25 

» 

7L 

>? 

15 

59 

Chap.  IX.        AND   SELF-FEKTILISED  FLOWEKS. 

Table  F — continued. 


m 


Viscaria     OCULATA — crossed    and    self-fertilised    flowers"! 

yielded  seeds  as  (by  weight) / 

Viscaria     OCULata  —  crossed    and    self-fertilised    flowers ) 

(crossed  capsules  compared  on  following  year  with  spon-> 

taneously  self-fertilised  capsules)  yielded  seeds  as  .      .      . ) 
Dianthus  OARYOPHyllus — crossed  and  self-fertilised  flowersi 

yielded  seeds  as J 

Tropjeolum     minus — crossed    and    self-fertilised    flowers^! 

yielded  seeds  as j 

Trop^eolum     tricolorum*  —  crossed    and    self-fertilised"! 

flowers  yielded  seeds  as / 

Limnanthes  douglasii — crossed  and  self-fertilised  flowers'! 

yielded  seeds  as  (about) J 

Sarothamnus  SCOPARIUS — crossed  and  self-fertilised  flowers  \ 

yielded  seeds  as J 

Ononis   minutissima — crossed    and   self-fertilised    flowers'! 

yielded  seeds  as J 

Cuphea    purpurea  —  crossed    and    self-fertilised   flowers'! 

yielded  seeds  as J 

Passiflora   gracilis — crossed    and    self-fertilised   flowers'! 

yielded  seeds  as ) 

Specularia  speculum — crossed  and  self-fertilised  flowers'! 

yielded  seeds  as / 

Lobelia  fulgens — 'Crossed  and  self-fertilised  flowers  yielded"! 

seeds  as  (about) j 

Nemophila   insignis — crossed    and    self- fertilised   flowers) 

yielded  seeds  as  (by  weight) J 

Borago   officinalis — crossed   and    self-fertilised   flowers 

yielded  seeds  as   

Nolana   prostrata  —  crossed     and   self-fertilised   flowers'! 

yielded  seeds  as j 

Petunia   violacea  —  crossed    and    self-fertilised    flowers'! 

yielded  seeds  as  (by  weight) j 

Nicotiana   tabacum — crossed    and    self-fertilised   flowers'! 

yielded  seeds  as  (by  weight) / 

Cyclamen   persicum  —  crossed  and  self-fertilised  flowers'! 

yielded  seeds  as   .  .  J 

Anagallis   collina  —  crossed    and    self-fertilised    flowers'! 

yielded  seeds  as j 

Canna  warscewiczi — crossed  and  self-fertilised  flowers  (on) 

three  generations  of  crossed  and  self-fertilised  plants  taken  > 

all  together)  yielded  seeds  as ) 


100  to 

38 

» 

)> 

58 

j> 

11 

92 

V 

j> 

92 

n 

>> 

115 

n 

>> 

100 

n 

n 

41 

■>■> 

ji 

65 

» 

j) 

113 

>» 

n 

85 

n 

?> 

72 

» 

n 

100 

5> 

» 

69 

j» 

» 

60 

n 

n 

100 

it 

11 

67 

n 

11 

150 

n 

j» 

38 

j» 

» 

96 

85 


*  Tropxolum  tricolorum  and 
Cuphea  purpurea  have  been  intro- 
duced into  this  table,  although 
seedlings  were  not  raised  from 
them ;  but  of  the  Cuphea  only 
six  crossed  and  six  self-ferti- 
lised capsules,  and  of  the  Tropse- 


olurn  only  six  crossed  and  eleven 
self-fertilised  capsules,  were  com- 
pared. A  larger  proportion  of 
the  self-fertilised  than  of  the 
crossed  flowers  of  the  Tjopseolum 
produced  fruit. 


324 


FERTILITY   OF   CROSSED 


Chap.  IX. 


A  second  table,  G,  gives  the  relative  fertility  of 
flowers  on  crossed  plants  again  cross-fertilised,  and  of 
flowers  on  self-fertilised  plants  again  self-fertilised, 
either  in  the  first  or  in  a  later  generation.  Here  two 
causes  combine  to  diminish  the  fertility  of  the  self- 
fertilised  flowers  ;  namely,  the  lesser  efficacy  of  pollen 
from  the  same  flower,  and  the  innate  lessened  fertility 
of  plants  derived  from  self-fertilised  seeds,  which  as  we 
have  seen  in  the  previous  Table  D  is  strongly  marked. 
The  fertility  was  determined  in  the  same  manner  as 
in  Table  F,  that  is,  by  the  average  number  of  seeds  per 
capsule  ;  and  the  same  remarks  as  before,  with  respect 
to  the  different  proportion  of  flowers  which  set  capsules 
when  they  are  cross-fertilised  and  self-fertilised,  are 
here  likewise  applicable. 


Table  G. — Relative  Fertility  of  Floivers  on  Crossed  and  Self- 
fertilised  Plants  of  the  First  or  some  succeeding  Generation  ;  the 
former  being  again  fertilised  ivith  Pollen  from  a  distinct  Plant, 
and  the  latter  again  with  their  own  Pollen.  Fertility  judged 
of  by  the  average  Number  of  Seeds  per  Cajoside.  Fertility  of 
Crossed  Flowers  taken  as  100. 


Ipomcea  purpurea — crossed  and  self- fertilised  flowers  on] 
the  crossed  and  self-fertilised  plants  of  the  1st  generation  > 
yielded  seeds  as J 

Ipomcea  purpurea — crossed  and  self-fertilised  flowers  on 
the  crossed  and  self-fertilised  plants  of  the  3rd  generation 
yielded  seeds  as 

Ipomcea  purpurea — crossed  and  self-fertilised  flowers  on 
the  crossed  and  self-fertilised  plants  of  the  4th  generation 
yielded  seeds  as 

Ipomcea  purpurea — crossed  and  self-fertilised  flowers  on 
the  crossed  and  self- fertilised  plants  of  the  5th  generation  > 
yielded  seeds  as ) 

Mimulus  luteus — crossed  and  self-fertilised  flowers  on  the) 
crossed  and  self- fertilised  plants  of  the  3rd  generation  I 
yielded  seeds  as  (by  weight) ) 

Mimulus  luteus — same  plants  treated  in  the  same  manner^ 
on  following  year  yielded  seeds  as  (by  weight)        .      .      .  f 

Mimulus  luteus — crossed  and  self-fertilised  flowers  on  the  J 
crossed  and  self- fertilised  plants  of  the  4th  generation  > 
yielded  seeds  as  (by  weight) J 


100  to 

93 

ii     ii 

94 

ii    »> 

94 

ii    ii 

107 

ii    ii 

65 

ii    ii 

34 

ii     n 

40 

Chap.  IX.         AND   SELF-FEETILISED   FLOWEKS. 
Table  G — continued. 


325 


Viola  tricolor — crossed  and  self-fertilised  flowers  on  the 
crossed  and  self-fertilised  plants  of  the  1st  generation 
yielded  seeds  as    

Dianthus  caryophyllus — crossed  and  self-fertilised  flowers 
on  the  crossed  and  self-fertilised  plants  of  the  1st  genera- 
tion yielded  seeds  as 

Dianthus  caryophyllus — flowers  on  self-fertilised  plants 
of  the  3rd  generation  crossed  by  intercrossed  plants,  and 
other  flowers  again  self-fertilised  yielded  seeds  as 

Dianthus  caryophyllus — flowers  on  self-fertilised  plants 
of  the  3rd  generation  crossed  by  a  fresh  stock,  and  other 
flowers  again  self-fertilised  yielded  seeds  as     ... 

Lathyrus  ODoratus — crossed  and  self-fertilised  flowers  on 
the  crossed  and  self-fertilised  plants  of  the  1st  generation 
yielded  seeds  as   

Lobelia  raMosa — crossed  and  self-fertilised  flowers  on  the 
crossed  and  self- fertilised  plants  of  the  1st  generation 
yielded  seeds  as  (by  weight) 

Petunia  violacea — crossed  and  self-fertilised  flowers  on 
the  crossed  and  self-fertilised  plants  of  the  1st  generation 
yielded  seeds  as  (by  weight) 

Petunia  violacea — crossed  and  self-fertilised  flowers  on 
the  crossed  and  self-fertilised  plants  of  the  4th  generation 
yielded  seeds  as  (by  weight) 

Petunia  violacea — flowers  on  self-fertilised  plants  of  the 
4th  generation  crossed  by  a  fresh  stock,  and  other  flowers 
again  self-fertilised  yielded  seeds  as  (by  weight)   . 

Nicotiana  tabacum — crossed  and  self-fertilised  flowers  on 
the  crossed  and  self- fertilised  plants  of  the  1st  generation 
yielded  seeds  as  (by  weight) 

Nicotiana  tabacum — flowers  on  self-fertilised  plants  of 
the  2nd  generation  crossed  by  intercrossed  plants,  and 
other  flowers  again  self-fertilised  yielded  seeds  as  (by  es- 
timation)   

Nicotiana  tabacum  —  flowers  on  self-fertilised  plants  of 
the  3rd  generation  crossed  by  a  fresh  stock,  and  other 
flowers  again  self-fertilised  yielded  seeds  as  (by  estimation) 

Anagallis  collina — flowers  on  a  red  variety  crossed  by  a 
blue  variety,  and  other  flowers  on  the  red  variety  self- 
fertilised  yielded  seeds  as j 

Canna  Warscewiczi — crossed  and  self-fertilised  flowers  on 
the  crossed  and  self-fertilised  plants  of  three  generations 
taken  together  yielded  seeds  as j 


100  to    69 
»     »     65 

.,     ,.  127 


»  jj     68 

5»  )>     72 

„  „     48 

»  »     97 

»  „  no 


As  both  these  tables  relate  to  the  fertility  of 
flowers  fertilised  by  pollen  from  another  plant  and  by 
their  own  pollen,  they  may  be  considered  together. 
The   difference   between   them    consists    in   the   self- 


326  FEKTILITY   OF   CEOSSED  Chap.  IX. 

fertilised  flowers  in  the  second  table,  G-,  being 
produced  by  self-fertilised  parents,  and  the  crossed 
flowers  by  crossed  parents,  which  in  the  later  generations 
had  become  somewhat  closely  inter-related,  and  had 
been  subjected  all  the  time  to  nearly  the  same  condi- 
tions. These  two  tables  include  fifty  cases  relating  to 
thirty-two  species.  The  flowers  on  many  other  species 
were  crossed  and  self-fertilised,  but  as  only  a  few  were 
thus  treated,  the  results  cannot  be  trusted,  as  far  as  fer- 
tility is  concerned,  and  are  not  here  given.  Some  other 
cases  have  been  rejected,  as  the  plants  were  in  an 
unhealthy  condition.  If  we  look  to  the  figures  in  the 
two  tables  expressing  the  ratios  between  the  mean 
relative  fertility  of  the  crossed  and  self-fertilised 
flowers,  we  see  that  in  a  majority  of  the  cases  (i.e., 
in  thirty- five  out  of  fifty)  flowers  fertilised  by  pollen 
from  a  distinct  plant  yield  more,  sometimes  many  more, 
seeds  than  flowers  fertilised  with  their  own  pollen  ;  and 
they  commonly  set  a  larger  proportion  of  capsules.  The 
degree  of  infertility  of  the  self-fertilised  flowers  differs 
extremely  in  the  different  species,  and  even,  as  we 
shall  see  in  the  section  on  self-sterile  plants,  in  the 
individuals  of  the  same  species,  as  well  as  under 
slightly  changed  conditions  of  life.  Their  fertility 
ranges  from  zero  to  fertility  equalling  that  of  the 
crossed  flowers ;  and  of  this  fact  no  explanation  can 
be  offered.  There  are  fifteen  cases  in  the  two  tables 
in  which  the  number  of  seeds  per  capsule  produced  by 
the  self- fertilised  flowers  equals  or  even  exceeds  that 
yielded  by  the  crossed  flowers.  Some  few  of  these 
cases  are,  I  believe,  accidental ;  that  is,  would  not 
recur  on  a  second  trial.  This  was  apparently  the 
case  with  the  plants  of  the  fifth  generation  of  Iponioea, 
and  in  one  of  the  experiments  with  Dianthus. 
Nicotiana   offers    the   most   anomalous   case    of  any, 


Chap.  IX.        AND   SELF-FERTILISED   FLOWERS.  327 

as  the  self-fertilised  flowers  on  the  parent-plants,  and 
on  their  descendants  of  the  second  and  third  genera- 
tions, produced  more  seeds  than  did  the  crossed 
flowers  ;  but  we  shall  recur  to  this  case  when  we  treat 
of  highly  self- fertile  varieties. 

It  might  have  been  expected  that  the  difference  in 
fertility  between  the  crossed  and  self-fertilised  flowers 
would  have  been  more  strongly  marked  in  Table  G-,  in 
which  the  plants  of  one  set  were  derived  from  self- 
fertilised  parents,  than  in  Table  F,  in  which  flowers  on 
the  parent-plants  were  self- fertilised  for  the  first  time. 
But  this  is  not  the  case,  as  far  as  my  scanty  materials 
allow  of  any  judgment.  There  is  therefore  no  evi- 
dence at  present,  that  the  fertility  of  plants  goes  on 
diminishing  in  successive  self-fertilised  generations, 
although  there  is  some  rather  weak  evidence  that 
this  does  occur  with  respect  to  their  height  or  growth. 
But  Ave  should  bear  in  mind  that  in  the  later  genera- 
tions the  crossed  plants  had  become  more  or  less  closely 
inter-related,  and  had  been  subjected  all  the  time  to 
nearly  uniform  conditions. 

It  is  remarkable  that  there  is  no  close  correspondence, 
either  in  the  parent-plants  or  in  the  successive  genera- 
tions, between  the  relative  number  of  seeds  produced 
by  the  crossed  and  self-fertilised  flowers,  and  the 
relative  powers  of  growth  of  the  seedlings  raised  from 
such  seeds.  Thus,  the  crossed  and  self-fertilised 
flowers  on  the  parent-plants  of  Ipomoea,  Gesneria, 
Salvia,  Limnanthes,  Lobelia  fulgens,  and  Nolana  pro- 
duced a  nearly  equal  number  of  seeds,  yet  the  plants 
raised  from  the  crossed  seeds  exceeded  considerably  in 
height  those  raised  from  the  self-fertilised  seeds. 
The  crossed  flowers  of  Linaria  and  Viscaria  yielded 
far  more  seeds  than  the  self-fertilised  flowers ;  and 
although  the  plants  raised  from  the  former  were  taller 
15 


328  FEKTILITY  OF   CEOSSED  Chap.  IX. 

than  those  from  the  latter,  they  were  not  so  in  any 
corresponding  degree.  With  Nicotiana  the  flowers 
fertilised  with  their  own  pollen  were  more  productive 
than  those  crossed  with  pollen  from  a  slightly  different 
variety;  yet  the  plants  raised  from  the  latter  seeds 
were  much  taller,  heavier,  and  more  hardy  than  those 
raised  from  the  self-fertilised  seeds.  On  the  other 
hand,  the  crossed  seedlings  of  Eschscholtzia  were 
neither  taller  nor  heavier  than  the  self-fertilised, 
although  the  crossed  flowers  were  far  more  productive 
than  the  self-fertilised.  But  the  best  evidence  of  a 
want  of  correspondence  between  the  number  of  seedy 
produced  by  crossed  and  self-fertilised  flowers,  and 
the  vigour  of  the  offspring  raised  from  them.,  is  afforded 
by  the  plants  of  the  Brazilian  and  European  stocks 
of  Eschscholtzia,  and  likewise  by  certain  individual 
plants  of  Reseda  odorata ;  for  it  might  have  been  ex- 
pected that  the  seedlings  from  plants,  the  flowers  of 
which  were  excessively  self-sterile,  would  have  profited 
in  a  greater  degree  by  a  cross,  than  the  seedlings  from 
plants  which  were  moderately  or  fully  self-fertile,  and 
therefore  apparently  had  no  need  to  be  crossed.  But 
no  such  result  followed  in  either  case :  for  instance, 
the  crossed  and  self-fertilised  offspring  from  a  highly 
self-fertile  plant  of  Reseda  odorata  were  in  average 
height  to  each  other  as  100  to  82 ;  whereas  the  similar 
offspring  from  an  excessively  self-sterile  plant  were  as 
100  to  92  in  average  height. 

With  respect  to  the  innate  fertility  of  the  plants 
of  crossed  and  self-fertilised  parentage,  given  in  the 
previous  Table  D — that  is,  the  number  of  seeds  pro- 
duced by  both  lots  when  their  flowers  were  fertilised 
in  the  same  manner, — nearly  the  same  remarks  are 
applicable,  in  reference  to  the  absence  of  any  close 
correspondence  between  their  fertility  and  powers  of 


Chap.  IX.        AND   SELF-FERTILISED   FLOWERS.  329 

growth,  as  in  the  case  of  the  plants  in  the  Tables  E 
and  G,  just  considered.  Thus  the  crossed  and  self -fer- 
tilised plants  of  Ipomoea,  Papaver,  Reseda  oclorata,  and 
Limnanthes  were  almost  equally  fertile,  yet  the  former 
exceeded  considerably  in  height  the  self-fertilised 
plants.  On  the  other  hand,  the  crossed  and  self-ferti- 
lised plants  of  Mimulus  and  Primula  differed  to  an 
extreme  degree  in  innate  fertility,  but  by  no  means  to 
a  corresponding  degree  in  height  or  vigour. 

In  all  the  cases  of  self-fertilised  flowers  included  in 
Tables  E,  F,  and  G,  these  were  fertilised  with  their 
own  pollen  ;  but  there  is  another  form  of  self-fertilisa- 
tion, viz.,  by  pollen  from  other  flowers  on  the  same 
plant;  but  this  latter  method  made  no  difference  in 
comparison  with  the  former  in  the  number  of  seeds 
produced,  or  only  a  slight  difference.  Neither  with 
Digitalis  nor  Dianthus  were  more  seeds  produced  by 
the  one  method  than  by  the  other,  to  any  trustworthy 
degree.  With  Ipomoea  rather  more  seeds,  in  the  pro- 
portion of  100  to  91,  were  produced  from  a  cross 
between  flowers  on  the  same  plant  than  from  strictly 
self-fertilised  flowers ;  but  I  have  reason  to  suspect  that 
the  result  was  accidental.  With  Origanum  vulgare, 
however,  a  cross  between  flowers  on  plants  propagated 
by  stolons  from  the  same  stock  certainly  increased 
slightly  their  fertility.  This  likewise  occurred,  as  we 
shall  see  in  the  next  section,  with  Eschscholtzia, 
perhaps  with  Corydalis  cava  and  Oncidium ;  but  not 
so  with  Bignonia,  Abutilon,  Tabernsemontana,  Senecio, 
and  apparently  Reseda  odorata. 

belf-sterile  Plants. 

The  cases  here  to  be  described  might  have  been 
introduced  in  Table  F,  which  gives  the  relative  fer- 
tility of  flowers  fertilised  with  their  own  pollen,  and 


330  SELF-STERILE  PLANTS.  Chap.  IX. 

with  that  from  a  distinct  plant ;  but  it  has  been  found 
more  convenient  to  keep  them  for  separate  discussion. 
The  present  cases  must  not  be  confounded  with  those 
to  be  given  in  the  next  chapter  relatively  to  flowers 
which  are  sterile  when  insects  are  excluded  ;  for  such 
sterility  depends  not  merely  on  the  flowers  being 
incapable  of  fertilisation  with  their  own  pollen,  but  on 
mechanical  causes,  by  which  their  pollen  is  prevented 
from  reaching  the  stigma,  or  on  the  pollen  and  stigma 
of  the  same  flower  being  matured  at  different  periods. 

In  the  seventeenth  chapter  of  my  'Variation  of 
Animals  and  Plants  under  Domestication 'I  had  occasion 
to  enter  fully  on  the  present  subject ;  and  I  will  there- 
fore here  give  only  a  brief  abstract  of  the  cases  there 
described,  but  others  must  be  added,  as  they  have  an 
important  bearing  on  the  present  work.  Kolreuter 
long  ago  described  plants  of  Verbaseum  phoeniceum 
which  during  two  years  were  sterile  with  their  own 
pollen,  but  were  easily  fertilised  by  that  of  four  other 
species ;  these  plants  however  afterwards  became  more 
or  less  self-fertile  in  a  strangely  fluctuating  manner. 
Mr.  Scott  also  found  that  this  species,  as  well  as  two  of 
its  varieties,  were  self-sterile,  as  did  Gartner  in  the 
case  of  Verbaseum  nigrum.  So  it  was.  according  to 
this  latter  author,  with  two  plants  of  Lobelia  fulgens, 
though  the  pollen  and  ovules  of  both  were  in  an 
efficient  state  in  relation  to  other  species.  Five  species 
of  Passiflora  and  certain  individuals  of  a  sixth  species 
have  been  found  sterile  with  their  own  pollen;  but  slight 
changes  in  their  conditions,  such  as  being  grafted  on 
another  stock  or  a  change  of  temperature,  rendered 
them  self-fertile.  Flowers  on  a  completely  self-im- 
potent plant  of  Passiflora  alata  fertilised  with  pollen 
from  its  own  self-impotent  seedlings  were  quite  fertile. 
Mr.  Scott,  and  afterwards  Mr.  Munro,  found  that  some 


Chap.  IX.  SELF-STEEILE   PLANTS.  331 

species  of  Oncidium  and  of  Maxillaria  cultivated  in  a 
hothouse  in  Edinburgh  were  quite  sterile  with  their 
own  pollen ;  and  Fritz  Miiller  found  this  to  be  the 
case  with  a  large  number  of  Orchidaceous  genera 
growing  in  their  native  home  of  South  Brazil.*  He 
also  discovered  that  the  pollen-masses  of  some  orchids 
acted  on  their  own  stigmas  like  a  poison ;  and  it 
appears  that  Gartner  formerly  observed  indications  of 
this  extraordinary  fact  in  the  case  of  some  other 
plants. 

Fritz  Muller  also  states  that  a  species  of  Bignonia 
and  Taberneemontana  echinata  are  both  sterile  with 
their  own  pollen  in  their  native  country  of  Brazil,  f 
Several  Amaryllidaceous  and  Liliaceous  plants  are  in 
the  same  predicament.  Hildebrand  observed  with  care 
Corydalis  cava,  and  found  it  completely  self-sterile ;  % 
but  according  to  Caspary  a  few  self-fertilised  seeds 
are  occasionally  produced :  Corydalis  halleri  is  only 
slightly  self-sterile,  and  C.  intermedia  not  at  all  so.  § 
In  another  Furnariaceous  genus,  Hypecoum,  Hildebrand 
observed  ||  that  H.  grandifiorum  was  highly  self-sterile, 
whilst  H.  proeumbens  was  fairly  self -fertile.  Thunbergia 
alata  kept  by  me  in  a  warm  greenhouse  was  self-sterile 
early  in  the  season,  but  at  a  later  period  produced 
many  spontaneously  self-fertilised  fruits.  So  it  was 
with  Papaver  vagum :  another  species,  P.  alpinum,  was 
found  by  Professor  H.  Hoffmann  to  be  quite  self- 
sterile  excepting  on  one  occasion; IF  whilst  P.  somni- 
ferum  has  been  with  me  always  completely  self-fertile. 

Eschscholtzia  californica.  —  This  species  deserves  a 
fuller   consideration.      A   plant   cultivated   by   Fritz 

*  '  Bot.  Zeittmg,'  1868,  p.  114.  §  'Bot.  Zeitung,'  June  27, 1873. 

t  Ibid.  1868,  p.  626,  and  1870,  ||    'Jahrb.   fur   wiss.   Botanik,' 

p.  274.  B.  vii.  p.  464. 

J  '  Beport  of  the  International  ^f   '  Zur    Speciesfrago,'    1875, 

Hort.  Congress,'  1S66.  p.  47. 


332  SELF-STEEILB   PLANTS.  Chap.  IX. 

Muller  in  South  Brazil  happened  to  flower  a  month  before 
any  of  the  others,  and  it  did  not  produce  a  single 
capsule.  This  led  him  to  make  further  observations 
during  the  next  six  generations,  and  he  found  that  all 
his  plants  were  completely  sterile,  unless  they  were 
crossed  by  insects  or  were  artificially  fertilised  with 
pollen  from  a  distinct  plant,  in  which  case  they  were 
completely  fertile.*  I  was  much  surprised  at  this  fact, 
as  I  had  found  that  English  plants,  when  covered  by 
a  net,  set  a  considerable  number  of  capsules  ;  and  that 
these  contained  seeds  by  weight,  compared  with  those 
on  plants  intercrossed  by  the  bees,  as  71  to  100. 
Professor  Hildebrand,  however,  found  this  species 
much  more  self-sterile  in  Germany  than  it  was  with 
me  in  England,  for  the  capsules  produced  by  self- 
fertilised  flowers,  compared  with  those  from  intercrossed 
flowers,  contained  seeds  in  the  ratio  of  only  11  to  100. 
At  my  request  Eritz  Miiller  sent  me  from  Brazil  seeds 
of  his  self-sterile  plants,  from  which  I  raised  seedlings. 
Two  of  these  were  covered  with  a  net,  and  one  produced 
spontaneously  only  a  single  capsule  containing  no  good 
seeds,  but  yet,  when  artificially  fertilised  with  its  own 
pollen,  produced  a  few  capsules.  The  other  plant  pro- 
duced spontaneously  under  the  net  eight  capsules,  one 
of  which  contained  no  less  than  thirty  seeds,  and  on 
an  average  about  ten  seeds  per  capsule.  Eight  flowers 
on  these  two  plants  were  artificially  self-fertilised,  and 
produced  seven  capsules,  containing  on  an  average 
twelve  seeds ;  eight  other  flowers  were  fertilised  with 
pollen  from  a  distinct  plant  of  the  Brazilian  stock,  and 
produced  eight  capsules,  containing  on  an  average 
about  eighty  seeds :  this  gives  a  ratio  of  15  seeds  for 
the   self-fertilised    capsules    to    100   for   the   crossed 


*  <Bot.  Zeitung,'  1868,  p.  115,  and  1869,  p.  223. 


Chap.  IX.  SELF-STEKILE   PLANTS.  333 

capsules.  Later  in  the  season  twelve  other  flowers  on 
these  two  plants  were  artificially  self-fertilised ;  but 
they  yielded  only  two  capsules,  containing  three  and 
six  seeds.  It  appears  therefore  that  a  lower  tem- 
perature than  that  of  Brazil  favours  the  self-fertility 
of  this  plant,  whilst  a  still  lower  temperature  lessens  it. 
As  soon  as  the  two  plants  which  had  been  covered  by 
the  net  were  uncovered,  they  were  visited  by  many 
bees,  and  it  was  interesting  to  observe  how  quickly 
they  became,  even  the  more  sterile  plant  of  the  two, 
covered  with  young  capsules.  On  the  following  year 
eight  flowers  on  plants  of  the  Brazilian  stock  of  self- 
fertilised  parentage  (i.e.,  grandchildren  of  the  plants 
which  grew  in  Brazil)  were  again  self-fertilised,  and 
produced  five  capsules,  containing  on  an  average  27*4 
seeds,  with  a  maximum  in  one  of  forty-two  seeds  ;  so 
that  their  self-fertility  had  evidently  increased  greatly 
by  being  reared  for  two  generations  in  England.  On 
the  whole  we  may  conclude  that  plants  of  the  Brazilian 
stock  are  much  more  self-fertile  in  this  country  than 
in  Brazil,  and  less  so  than  plants  of  the  English  stock 
in  England ;  so  that  the  plants  of  Brazilian  parentage 
retained  by  inheritance  some  of  their  former  sexual 
constitution.  Conversely,  seeds  from  English  plants 
sent  by  me  to  Fritz  Miiller  and  grown  in  Brazil,  were 
much  more  self -fertile  than  his  plants  which  had  been 
cultivated  there  for  several  generations  ;  but  he  informs 
me  that  one  of  the  plants  of  English  parentage  which 
did  not  flower  the  first  year,  and  was  thus  exposed  for 
two  seasons  to  the  climate  of  Brazil,  proved  quite  self- 
sterile,  like  a  Brazilian  plant,  showing  how  quickly 
the  climate  had  acted  on  its  sexual  constitution. 

Ahutilon  darwinii. — Seeds  of  this  plant  were  sent 
me  by  Fritz  Miiller,  who  found  it,  as  well  as  some 
other  species  of  the  same  genus,  quite  sterile  in  its 


334  SELF-STERILE   PLANTS.  Chap.  IX. 

native  home  of  South  Brazil,  unless  fertilised  with 
pollen  from  a  distinct  plant,  either  artificially  or 
naturally  by  humming-birds.*  Several  plants  were 
raised  from  these  seeds  and  kept  in  the  hothouse. 
They  produced  flowers  very  early  in  the  spring,  and 
twenty  of  them  were  fertilised,  some  with  pollen  from 
the  same  flower,  and  some  with  pollen  from  other 
flowers  on  the  same  plants ;  but  not  a  single  capsule 
was  thus  produced,  yet  the  stigmas  twenty-seven  hours 
after  the  application  of  the  pollen  were  penetrated  by 
the  pollen-tubes.  At  the  same  time  nineteen  flowers 
were  crossed  with  pollen  from  a  distinct  plant,  and 
these  produced  thirteen  capsules,  all  abounding  with 
fine  seeds.  A  greater  number  of  capsules  would  have 
been  produced  by  the  cross,  had  not  some  of  the  nine- 
teen flowers  been  on  a  plant  which  was  afterwards 
proved  to  be  from  some  unknown  cause  completely 
sterile  with  pollen  of  any  kind.  Thus  far  these  plants 
behaved  exactly  like  those  in  Brazil ;  but  later  in  the 
season,  in  the  latter  part  of  May  and  in  June,  they 
began  to  produce  under  a  net  a  few  spontaneous^ 
self-fertilised  capsules.  As  soon  as  this  occurred, 
sixteen  flowers  were  fertilised  with  their  own  pollen, 
and  these  produced  five  capsules,  containing  on  an 
average  3 "  4  seeds.  At  the  same  time  I  selected  by 
chance  four  capsules  from  the  uncovered  plants  grow- 
ing close  by,  the  flowers  of  which  I  had  seen  visited 
by  humble-bees,  and  these  contained  on  an  average 
21  •  5  seeds ;  so  that  the  seeds  in  the  naturally  inter- 
crossed capsules  to  those  in  the  self-fertilised  capsules 
were  as  100  to  16.  The  interesting  point  in  this  case 
is  that  these  plants,  which  were  unnaturally  treated 
by  being  grown  in  pots  in  a  hothouse,  under  another 

*  '  Jenaische  Zeitsckr.  fur  Naturwiss.'  B.  vii.  1872,  p.  22,  and  1 873, 
p.  441. 


Chav.  IX.  SELF-STEEILE   PLANTS.  335 

hemisphere,  with  a  complete  reversal  of  the  seasons, 
were  thus  rendered  slightly  self-fertile,  whereas  they 
seem  always  to  be  completely  self-sterile  in  their 
native  home. 

Senecio  cruentus  (greenhouse  varieties,  commonly 
called  Cinerarias,  probably  derived  from  several  fruticose 
or  herbaceous  species  much  intercrossed*). — Two  purple- 
flowered  varieties  were  placed  under  a  net  in  the 
greenhouse,  and  four  corymbs  on  each  were  re- 
peatedly brushed  with  flowers  from  the  other  plant, 
so  that  their  stigmas  were  well  covered  with  each 
other's  pollen.  Two  of  the  eight  corymbs  thus  treated 
produced  very  few  seeds,  but  the  other  six  produced 
on  an  average  41  •  3  seeds  per  corymb,  and  these  ger- 
minated well.  The  stigmas  on  four  other  corymbs  on 
both  plants  were  well  smeared  with  pollen  from  the 
flowers  on  their  own  corymbs ;  these  eight  corymbs 
produced  altogether  ten  extremely  poor  seeds,  which 
proved  incapable  of  germinating.  I  examined  many 
flowers  on  both  plants,  and  found  the  stigmas  sponta- 
neously covered  with  pollen ;  but  they  produced  not  a 
single  seed.  These  plants  were  afterwards  left  un- 
covered in  the  same  house  where  many  other  Cinerarias 
were  in  flower ;  and  the  flowers  were  frequently  visited 
by  bees.  They  then  produced  plenty  of  seed,  but  one 
of  the  two  plants  less  than  the  other,  as  this  species 
shows  some  tendency  to  be  dioecious. 

The  trial  was  repeated  on  another  variety  with 
white  petals  tipped  with  red.  Many  stigmas  on  two 
corymbs  were  covered  with  pollen  from  the  foregoing 
purple  variety,  and  these  produced  eleven  and  twenty  - 

*  I   am   much  obliged  to  Mr.  lieves  that  Senecio  cruentus,   tus- 

Moore  and  to  Mr.  Tbiselfcon  Dyer  silaginis,   aud    perhaps   heritii-ri, 

for  giving   me   information    with  maderensis  and  popuhfolius  have 

respect  to  the  varieties  ou  winch  all  been  more  or  less  blended  to* 

I  experimented.     Mr.  Moore  bo-  gether  in  our  Cinerarias. 


336  SELF-STEEILE   PLANTS.  Chap.  IX 

two  seeds,  which,  germinated  well.  A  large  number  of 
the  stigmas  on  several  of  the  other  corymbs  were  re- 
peatedly smeared  with  pollen  from  their  own  corymb ; 
but  they  yielded  only  five  very  poor  seeds,  which  were 
incapable  of  germination.  Therefore  the  above  three 
plants  belonging  to  two  varieties,  though  growing 
vigorously  and  fertile  with  pollen  from  either  of  the 
other  two  plants,  were  utterly  sterile  with  pollen  from 
other  flowers  on  the  same  plant. 

Reseda  odorata. — Having  observed  that  certain  in- 
dividuals were  self-sterile,  I  covered  during  the 
summer  of  1868  seven  plants  under  separate  nets,  and 
will  call  these  plants  A,  B,  C,  D,  E,  F,  G.  They  all 
appeared  to  be  quite  sterile  with  their  own  pollen, 
but  fertile  with  that  of  any  other  plant. 

Fourteen  flowers  on  A  were  crossed  with  pollen 
from  B  or  C,  and  produced  thirteen  fine  capsules. 
Sixteen  flowers  were  fertilised  with  pollen  from  other 
flowers  on  the  same  plant,  but  yielded  not  a  single 
capsule. 

Fourteen  flowers  on  B  were  crossed  with  pollen 
from  A,  C,  or  D,  and  all  produced  capsules ;  some  of 
these  were  not  very  fine,  yet  they  contained  plenty  of 
seeds.  Eighteen  flowers  were  fertilised  with  pollen 
from  other  flowers  on  the  same  plant,  and  produced 
not  one  capsule. 

Ten  flowers  on  C  were  crossed  with  pollen  from  A, 
B,  D,  or  E,  and  produced  nine  fine  capsules.  Nineteen 
flowers  were  fertilised  with  pollen  from  other  flowers 
on  the  same  plant,  and  produced  no  capsules. 

Ten  flowers  on  D  were  crossed  with  pollen  from 
A,  B,  0,  or  E,  and  produced  nine  fine  capsules. 
Eighteen  flowers  were  fertilised  with  pollen  from  other 
flowers  on  the  same  plant,  and  produced  no  capsules. 

Seven  flowers  on  E  were  crossed  with  pollen  from 


Chap.  IX.  6ELF-STEKILE   PLANTS.  337 

A,  C,  or  D,  and  all  produced  fine  capsules.  Eight 
flowers  were  fertilised  with  pollen  from  other  flowers 
on  the  same  plant,  and  produced  no  capsules. 

On  the  plants  F  and  Gr  no  flowers  were  crossed,  but 
very  many  (number  not  recorded)  were  fertilised  with 
pollen  from  other  flowers  on  the  same  plants,  and  these 
did  not  produce  a  single  capsule. 

We  thus  see  that  fifty-five  flowers  on  five  of  the 
above  plants  were  reciprocally  crossed  in  various  ways ; 
several  flowers  on  each  of  these  plants  being  ferti- 
lised with  pollen  from  several  of  the  other  plants. 
These  fifty-five  flowers  produced  fifty-two  capsules, 
almost  all  of  which  were  of  full  size  and  contained 
an  abundance  of  seeds.  On  the  other  hand,  seventy- 
nine  flowers  (besides  many  others  not  recorded)  were 
fertilised  with  pollen  from  other  flowers  on  the  same 
plants,  and  these  did  not .  produce  a  single  capsule. 
In  one  case  in  which  I  examined  the  stigmas  of  the 
flowers  fertilised  with  their  own  pollen,  these  were 
penetrated  by  the  pollen-tubes,  although  such  pene- 
tration produced  no  effect.  Pollen  falls  generally, 
and  I  believe  always,  from  the  anthers  on  the  stigmas 
of  the  same  flower;  yet  only  three  out  of  the 
above  seven  protected  plants  produced  spontaneously 
any  capsules,  and  these  it  might  have  been  thought 
must  have  been  self-fertilised.  There  were  altogether 
seven  such  capsules ;  but  as  they  were  all  seated  close 
to  the  artificially  crossed  flowers,  I  can  hardly  doubt 
that  a  few  grains  of  foreign  pollen  had  accidentally 
fallen  on  their  stigmas.  Besides  the  above  seven 
plants,  four  others  were  kept  covered  under  the  same 
large  net ;  and  some  of  these  produced  here  and 
there  in  the  most  capricious  manner  little  groups 
of  capsules ;  and  this  makes  me  believe  that  a  bee, 
many  of  which  settled  on  the  outside  of  the  net,  being 


338  SELF-STEEILE   PLANTS.  Chap.  IX. 

attracted  by  the  odour,  had  on  some  one  occasion 
found  an  entrance,  and  had  intercrossed  a  few  of  the 
flowers. 

In  the  spring  of  1869  four  plants  raised  from  fresh 
seeds  were  carefully  protected  under  separate  nets; 
and  now  the  result  was  widely  different  to  what  it  was 
before.  Three  of  these  protected  plants  became  actually 
loaded  with  capsules,  especially  during  the  early  part 
of  the  summer ;  and  this  fact  indicates  that  tempera- 
ture produces  some  effect,  but  the  experiment  given 
in  the  following  paragraph  shows  that  the  innate  con- 
stitution of  the  plant  is  a  far  more  important  element. 
The  fourth  plant  produced  only  a  few  capsules,  many 
of  them  of  small  size ;  yet  it  was  far  more  self-fertile 
than  any  of  the  seven  plants  tried  during  the  previous 
year.  The  flowers  on  four  small  branches  of  this 
semi-self-sterile  plant  were  smeared  with  pollen  from 
one  of  the  other  plants,  and  they  all  produced  fine 
capsules. 

As  I  was  much  surprised  at  the  difference  in  the 
results  of  the  trials  made  during  the  two  previous 
years,  six  fresh  plants  were  protected  by  separate  nets 
in  the  year  1870.  Two  of  these  proved  almost  com- 
pletely self- sterile,  for  on  carefully  searching  them  I 
found  only  three  small  capsules,  each  containing  either 
one  or  two  seeds  of  small  size,  which,  however,  ger- 
minated. A  few  flowers  on  both  these  plants  were 
reciprocally  fertilised  with  each  other's  pollen,  and 
a  few  with  pollen  from  one  of  the  following  self- 
fertile  plants,  and  all  these  flowers  produced  fine 
capsules.  The  four  other  plants  whilst  still  remaining 
protected  beneath  the  nets  presented  a  wonderful 
contrast  (though  one  of  them  in  a  somewhat  less 
degree  than  the  others),  for  they  became  actually 
covered  with  spontaneously  self-fertilised  capsules,  as 


Chap.  IX.  SELF-STERILE   PLANTS.  339 

numerous  as,  or  very  nearly  so,  and  as  fine  as  those 
on  the  unprotected  plants  growing  near. 

The  above  three  spontaneously  self-fertilised  cap- 
sules produced  by  the  two  almost  completely  self- 
sterile  plants,  contained  altogether  five  seeds ;  and 
from  these  I  raised  in  the  following  year  (1871)  five 
plants,  which  were  kept  under  separate  nets.  They 
grew  to  an  extraordinarily  large  size,  and  on  August 
29th  were  examined.  At  first  sight  they  appeared 
entirely  destitute  of  capsules  ;  but  on  carefully  search- 
ing their  many  branches,  two  or  three  capsules  were 
found  on  three  of  the  plants,  half-a-dozen  on  the 
fourth,  and  about  eighteen  on  the  fifth  plant.  But  all 
these  capsules  were  small,  some  being  empty ;  the 
greater  number  contained  only  a  single  seed,  and  very 
rarely  more  than  one.  After  this  examination  the 
nets  were  taken  off,  and  the  bees  immediately  carried 
pollen  from  one  of  these  almost  self-sterile  plants 
to  the  other,  for  no  other  plants  grew  near.  After  a 
few  weeks  the  ends  of  the  branches  on  all  five  plants 
became  covered  with  capsules,  presenting  a  curious 
contrast  with  the  lower  and  naked  parts  of  the  same 
long  branches.  These  five  plants  therefore  inherited 
almost  exactly  the  same  sexual  constitution  as  their 
parents ;  and  without  doubt  a  self-sterile  race  of 
Mignonette  could  have  been  easily  established. 

Reseda  lutea. — Plants  of  this  species  were  raised 
from  seeds  gathered  from  a  group  of  wild  plants  grow- 
ing at  no  great  distance  from  my  garden.  After 
casually  observing  that  some  of  these  plants  were  self- 
sterile,  two  plants  taken  by  hazard  were  protected 
under  separate  nets.  One  of  these  soon  became 
covered  with  spontaneously  self-fertilised  capsules,  as 
numerous  as  those  on  the  surrounding  unprotected 
plants ;    so   that   it   was   evidently   quite   self-fertile. 


340  SELF-STEKILE   PLANTS.  Chap.  IX. 

The  other  plant  was  partially  self-sterile,  producing 
very  few  capsules,  many  of  which  were  of  small 
size.  When,  however,  this  plant  had  grown  tall, 
the  uppermost  branches  became  pressed  against  the 
net  and  grew  crooked,  and  in  this  position  the  bees- 
were  able  to  suck  the  flowers  through  the  meshes,  and 
brought  pollen  to  them  from  the  neighbouring  plants. 
These  branches  then  became  loaded  with  capsules ; 
the  other  and  lower  branches  remaining  almost  bare. 
The  sexual  constitution  of  this  species  is  therefore 
similar  to  that  of  Reseda  odorata. 

Concluding/  Remarks  on  self -sterile  Plants. 

In  order  to  favour  as  far  as  possible  the  self-fer- 
tilisation of  some  of  the  foregoing  plants,  all  the 
flowers  on  Reseda  odorata  and  some  of  those  on  the 
Abutilon  were  fertilised  with  pollen  from  other 
flowers  on  the  same  plant,  instead  of  with  their  own 
pollen,  and  in  the  case  of  the  Senecio  with  pollen  from 
other  flowers  on  the  same  corymb ;  but  this  made  no 
difference  in  the  result.  Fritz  Miiller  tried  both  kinds 
of  self- fertilisation  in  the  case  of  Bignonia,  Tabernse- 
montana  and  Abutilon,  likewise  with  no  difference  in 
the  result.  With  Eschscholtzia,  however,  he  found 
that  pollen  from  other  flowers  on  the  same  plant 
was  a  little  more  effective  than  pollen  from  the 
same  flower.  So  did  Hildebrand*  in  Germany ;  as 
thirteen  out  of  fourteen  flowers  of  Eschscholtzia  thus 
fertilised  set  capsules,  these  containing  on  an  average 
9  •  5  seeds  ;  whereas  only  fourteen  flowers  out  of  twenty- 
one  fertilised  with  their  own  pollen  set  capsules, 
these  containing  on  an  average  9  ■  0  seeds.    Hildebrand 


*  '  Piing&heim's  Jalirbuch.  fur  sviss.  Botanik,'  vii.  p.  467. 


Chap.  IX.  SELF-STEKILE   PLANTS.  341 

found  a  trace  of  a  similar  difference  with  Corydalis 
cava,  as  did  Fritz  Miiller  with  an  Oncidium.* 

In  considering  the  several  cases  above  given  of 
complete  or  almost  complete  self-sterility,  we  are  first 
struck  with  their  wide  distribution  throughout  the 
vegetable  kingdom.  Their  number  is  not  at  present 
large,  for  they  can  be  discovered  only  by  protecting 
plants  from  insects  and  then  fertilising  them  with 
pollen  from  another  plant  of  the  same  species  and  with 
their  own  pollen ;  and  the  latter  must  be  proved  to 
be  in  an  efficient  state  by  other  trials.  Unless  all 
this  be  done,  it  is  impossible  to  know  whether  their 
self-sterility  may  not  be  due  to  the  male  or  female 
reproductive  organs,  or  to  both,  having  been  affected 
by  changed  conditions  of  life.  As  in  the  course  of  my 
experiments  I  have  found  three  new  cases,  and  as  Fritz 
Miiller  has  observed  indications  of  several  others,  it  is 
probable  that  they  will  hereafter  be  proved  to  be  far 
from  rare.f 

As  with  plants  of  the  same  species  and  parentage, 
some  individuals  are  self-sterile  and  others  self-fertile, 
of  which  fact  Reseda  odorata  offers  the  most  striking 
instances,  it  is  not  at  all  surprising  that  species  of 
the  same  genus  differ  in  this  same  manner.  Thus 
Verbascum  phoeniceum  and  nigrum  are  self- sterile,  whilst 
V.  thapsus  and  lychnitis  are  quite  self-fertile,  as  I 
know  by  trial.  There  is  the  same  difference  between 
some  of  the  species  of  Papaver,  Corydalis,  and  of  other 
genera.  Nevertheless,  the  tendency  to  self-sterility 
certainly  runs  to  a  certain  extent  in  groups,  as  we  see 


'  Variation    under   Domesti-  Chronicle,'  1868,  p.   1286)  states 

cation,'  chap.  xvii.  2nd  edit.  vol.  that  Lilium  auratum,  Impatiens 

ii.  pp.  113-115.  pallida  and  fulva,  and  Fursythia 

f  Mr.  Wilder,  the  editor  of  a  viridissima,   cannot  be  fertilised 

horticultural  journal  in  theUnited  with  their  osvn  pollen. 
States    (quoted    in    '  Gardeuers' 


342  SELF-STEEILE   PLANTS.  Chap.  IX 

in  the  genus  Passiflora,  and  with  the  Vandese  amongst 
Orchids. 

Self-sterility  differs  much  in  degree  in  different 
plants.  In  those  extraordinary  cases  in  which  pollen 
from  the  same  flower  acts  on  the  stigma  like  a  poison, 
it  is  almost  certain  that  the  plants  would  never  yield  a 
single  self-fertilised  seed.  Other  plants,  like  Corydalis 
cava,  occasionally,  though  very  rarely,  produce  a  few 
self-fertilised  seeds.  A  large  number  of  species,  as 
may  be  seen  in  Table  F,  are  less  fertile  with  their  own 
pollen  than  with  that  from  another  plant ;  and  lastly, 
some  species  are  perfectly  self-fertile.  Even  with  the 
individuals  of  the  same  species,  as  just  remarked, 
some  are  utterly  self-sterile,  others  moderately  so,  and 
some  perfectly  self-fertile.  The  cause,  whatever  it  may 
be,  which  renders  many  plants  more  or  less  sterile 
with  their  own  pollen,  that  is,  when  they  are  self- 
fertilised,  must  be  different,  at  least  to  a  certain  extent, 
from  that  which  determines  the  difference  in  height, 
vigour,  and  fertility  of  the  seedlings  raised  from  self- 
fertilised  and  crossed  seeds ;  for  we  have  already 
seen  that  the  two  classes  of  cases  do  not  by  any  means 
run  parallel.  This  want  of  parallelism  would  be 
intelligible,  if  it  could  be  shown  that  self-sterility 
depended  solely  on  the  incapacity  of  the  pollen-tubes 
to  penetrate  the  stigma  of  the  same  flower  deeply 
enough  to  reach  the  ovules  ;  whilst  the  greater  or  less 
vigorous  growth  of  the  seedlings  no  doubt  depends  on 
the  nature  of  the  contents  of  the  pollen-grains  and 
ovules.  Now  it  is  certain  that  with  some  plants  the 
stigmatic  secretion  does  not  properly  excite  the  pollen- 
grains,  so  that  the  tubes  are  not  properly  developed, 
if  the  pollen  is  taken  from  the  same  flower.  This  is 
the  case  according  to  Fritz  Muller  with  Eschscholtzia, 
for  he  found  that  the  pollen-tubes  did  not  penetrate 


Chap.  IX.  SELF-STERILE   PLANTS.  343 

the  stigma  deeply  ;*  and  with  the  Orchidaceous  genus 
Notylia  they  failed  altogether  to  penetrate  it. 

With  dimorphic  and  trimorphic  species,  an  illegiti- 
mate union  between  plants  of  the  same  form  presents 
the  closest  analogy  with  self-fertilisation,  whilst  a 
legitimate  union  closely  resembles  cross-fertilisation ; 
and  here  again  the  lessened  fertility  or  complete 
sterility  of  an  illegitimate  union  depends,  at  least  in 
part,  on  the  incapacity  for  interaction  between  the 
pollen-grains  and  stigma.  Thus  with  Linum  grandi- 
florum,  as  I  have  elsewhere  shown,  f  not  more  than  two 
or  three  out  of  hundreds  of  pollen-grains,  either  of  the 
long-styled  or  short-styled  form,  when  placed  on  the 
stigma  of  their  own  form,  emit  their  tubes,  and  these 
do  not  penetrate  deeply;  nor  does  the  stigma  itself 
change  colour,  as  occurs  when  it  is  legitimately 
fertilised. 

On  the  other  hand  the  difference  in  innate  fertility, 
as  well  as  in  growth  between  plants  raised  from  crossed 
and  self-fertilised  seeds,  and  the  difference  in  fertility 
and  growth  between  the  legitimate  and  illegitimate 
offspring  of  dimorphic  and  trimorphic  plants,  must 
depend  on  some  incompatibility  between  the  sexual 
elements  contained  within  the  pollen-grains  and  ovules, 
as  it  is  through  their  unioD  that  new  organisms  are 
developed. 

If  we  now  turn  to  the  more  immediate  cause  of 
self-sterility,  we  clearly  see  that  in  most  cases  it  is  de- 
termined by  the  conditions  to  which  the  plants  have 
been  subjected.  Thus  Eschscholtzia  is  completely  self- 
sterile  in  the  hot  climate  of  Brazil,  but  is  perfectly 
fertile  there  with  the  pollen  of  any  other  individual. 
The  offspring  of  Brazilian  plants  became  in  England 

*  '  Bot.  Zcitung,'  18G8,  pp.  114,  f  '  Journal  of  Linn.  Soc.  Bot. 

115.  vol.  vii.  1So3,  pp.  73-75. 


344  SELF-STERILE  PLANTS.  Chap.  IX 

in  a  single  generation  partially  self-fertile,  and  still 
more  so  in  the  second  generation.  Conversely,  the 
offspring  of  English  plants,  after  growing  for  two 
seasons  in  Brazil,  became  in  the  first  generation  quite 
self-sterile.  Again,  Abutilon  darwinii,  which  is  self- 
sterile  in  its  native  home  of  Brazil,  became  mode- 
rately self-fertile  in  a  single  generation  in  an  English 
hothouse.  Some  other  plants  are  self-sterile  during  the 
early  part  of  the  year,  and  later  in  the  season  become 
self-fertile.  Passijlora  alata  lost  its  self-sterility  when 
grafted  on  another  species.  With  Keseda,  however, 
in  which  some  individuals  of  the  same  parentage  are 
self-sterile  and  others  are  self-fertile,  we  are  forced  in 
our  ignorance  to  speak  of  the  cause  as  due  to  spon- 
taneous variability  ;  but  we  should  remember  that  the 
progenitors  of  these  plants,  either  on  the  male  or 
female  side,  may  have  been  exposed  to  somewhat 
different  conditions.  The  power  of  the  environment 
thus  to  affect  so  readily  and  in  so  peculiar  a  manner 
the  reproductive  organs,  is  a  fact  which  has  many 
important  bearings ;  and  I  have  therefore  thought 
the  foregoing  details  worth  giving.  For  instance,  the 
sterility  of  many  animals  and  plants  under  changed 
conditions  of  life,  such  as  confinement,  evidently  come? 
within  the  same  general  principle  of  the  sexual 
system  being  easily  affected  by  the  environment.  It 
has  already  been  proved,  that  a  cross  between  plants 
which  have  been  self-fertilised  or  intercrossed  during 
several  generations,  having  been  kept  all  the  time 
under  closely  similar  conditions,  does  not  benefit 
the  offspring ;  and  on  the  other  hand,  that  a  cross 
between  plants  that  have  been  subjected  to  different 
conditions  benefits  the  offspring  to  an  extraordinary 
degree.  We  may  therefore  conclude  that  some  degree 
of  differentiation  in  the  sexual  system  is  necessary  for 


Chap.  IX.  SELF-STERILE   PLANTS.  345 

the  full  fertility  of  the  parent-plants  and  for  the  full 
vigour  of  their  offspring.  It  seems  also  probable  that 
with  those  plants  which  are  capable  of  complete  self- 
fertilisation,  the  male  and  female  elements  and  organs 
already  differ  to  an  extent  sufficient  to  excite  their 
mutual  interaction  ;  but  that  when  such  plants  are 
taken  to  another  country,  and  become  in  consequence 
self-sterile,  their  sexual  elements  and  organs  are  so 
acted  on  as  to  be  rendered  too  uniform  for  such  inter- 
action, like  those  of  a  self-fertilised  plant  long 
cultivated  under  the  same  conditions.  Conversely,  we 
may  further  infer  that  plants  which  are  self-sterile  in 
their  native  country,  but  become  self-fertile  under 
changed  conditions,  have  their  sexual  elements  so  acted 
on,  that  they  become  sufficiently  differentiated  for 
mutual  interaction. 

We  know  that  self-fertilised  seedlings  are  inferior  in 
many  respects  to  those  from  a  cross ;  and  as  with 
plants  in  a  state  of  nature  pollen  from  the  same 
flower  can  hardly  fail  to  be  often  left  by  insects  or  by 
the  wind  on  the  stigma,  it  seems  at  first  sight  highly 
probable  that  self-sterility  has  been  gradually  acquired 
through  ifatural  selection  in  order  to  prevent  self- 
fertilisation.  It  is  no  valid  objection  to  this  belief 
that  the  structure  of  some  flowers,  and  the  dichogamous 
condition  of  many  others,  suffice  to  prevent  the  pollen 
reaching  the  stigma  of  the  same  flower;  for  we  should 
remember  that  with  most  species  many  flowers 
expand  at  the  same  time,  and  that  pollen  from  the 
same  plant  is  equally  injurious  or  nearly  so  as 
that  from  the  same  flower.  Nevertheless,  the  belief 
that  self-sterility  is  a  quality  which  has  been  gradually 
acquired  for  the  special  purpose  of  preventing  self- 
fertilisation  must,  I  believe,  be  rejected.  In  the 
first  place,  there  is  no  close  correspondence  in  degree 


346  SELF-STERILE   PLANTS.  Chap.  IX. 

between  the  sterility  of  the  parent-plants  when  self- 
fertilised,  and  the  extent  to  which  their  offspring  suffer 
in  vigour  by  this  process ;  and  some  such  correspon- 
dence might  have  been  expected  if  self-sterility  had 
been  acquired  on  account  of  the  injury  caused  by  self- 
fertilisation.  The  fact  of  individuals  of  the  same 
parentage  differing  greatly  in  their  degree  of  self- 
sterility  is  likewise  opposed  to  such  a  belief;  unless, 
indeed,  we  suppose  that  certain  individuals  have 
been  rendered  self-sterile  to  favour  intercrossing, 
whilst  other  individuals  have  been  rendered  self- 
fertile  to  ensure  the  propagation  of  the  species.  The 
fact  of  self-sterile  individuals  appearing  only  occa- 
sionally, as  in  the  case  of  Lobelia,  does  not  counte- 
nance this  latter  view.  But  the  strongest  argument 
against  the  belief  that  self-sterility  has  been  acquired 
to  prevent  self-fertilisation,  is  the  immediate  and 
powerful  effect  of  changed  conditions  in  either  causing 
or  in  removing  self-sterility.  We  are  not  therefore 
justified  in  admitting  that  this  peculiar  state  of  the 
reproductive  system  has  been  gradually  acquired 
through  natural  selection ;  but  we  must  look  at  it  as 
an  incidental  result,  dependent  on  the  conditions  to 
which  the  plants  have  been  subjected,  like  the  ordinary 
sterility  caused  in  the  case  of  animals  by  confinement, 
and  in  the  case  of  plants  by  too  much  manure,  heat,  &c. 
I  do  not,  however,  wish  to  maintain  that  self- sterility 
may  not  sometimes  be  of  service  to  a  plant  in  preventing 
self-fertilisation ;  but  there  are  so  many  other  means 
by  which  this  result  might  be  prevented  or  rendered 
difficult,  including  as  we  shall  see  in  the  next  chapter 
the  prepotency  of  pollen  from  a  distinct  individual 
over  a  plant's  own  pollen,  that  self-sterility  seems  an 
almost  superfluous  acquirement  for  this  purpose. 

Finally,  the  most  interesting  point  in  regard  to  self- 


Chap.  IX.  SELF-FEETILE   VARIETIES.  347 

sterile  plants  is  the  evidence  which  they  afford  of  the 
advantage,  or  rather  of  the  necessity,  of  some  degree  or 
kind  of  differentiation  in  the  sexual  elements,  in  order 
that  they  should  unite  and  give  birth  to  a  new  being. 
It  was  ascertained  that  the  five  plants  of  Reseda  odorata 
which  were  selected  by  chance,  could  be  perfectly 
fertilised  by  pollen  taken  from  any  one  of  them,  but 
not  by  their  own  pollen  ;  and  a  few  additional  trials 
were  made  with  some  other  individuals,  which  I  have 
not  thought  worth  recording.  So  again,  Hildebrand 
and  Fritz  Miiller  frequently  speak  of  self-sterile  plants 
being  fertile  with  the  pollen  of  any  other  individual ; 
and  if  there  had  been  any  exceptions  to  the  rule,  these 
could  hardly  have  escaped  their  observation  and  my 
own.  We  may  therefore  confidently  assert  that  a 
self-sterile  plant  can  be  fertilised  by  the  pollen  of  any 
one  out  of  a  thousand  or  ten  thousand  individuals  of 
the  same  species,  but  not  by  its  own.  Now  it  is 
obviously  impossible  that  the  sexual  organs  and 
elements  of  every  individual  can  have  been  specialised 
with  respect  to  every  other  individual.  But  there 
is  no  difficulty  in  believing  that  the  sexual  elements 
of  each  differ  slightly  in  the  same  diversified  manner 
as  do  their  external  characters ;  and  it  has  often  been 
remarked  that  no  two  individuals  are  absolutely 
alike.  Therefore  we  can  hardly  avoid  the  conclusion, 
that  differences  of  an  analogous  and  indefinite  nature 
in  the  reproductive  system  are  sufficient  to  excite  the 
mutual  action  of  the  sexual  elements,  and  that  unless 
there  be  such  differentiation  fertility  fails. 

The  appearance  of  highly  self -fertile  Varieties. — We 
have  just  seen  that  the  degree  to  which  flowers  are 
capable  of  being  fertilised  with  their  own  pollen  differs 
much,  both  with  the  species  of  the  same  genus,  and 


348  SELF-FERTILE   VARIETIES.  Chap.  IX. 

sometimes  with  the  individuals  of  the  same  speeies. 
Some  allied  cases  of  the  appearance  of  varieties  which, 
when  self-fertilised,  yield  more  seed  and  produce  off- 
spring growing  taller  than  their  self-fertilised  parents, 
or  than  the  intercrossed  plants  of  the  corresponding- 
generation,  will  now  be  considered. 

Firstly,  in  the  third  and  fourth  generations  of 
Mimulus  luteus,  a  tall  variety,  often  alluded  to, 
having  large  white  flowers  blotched  with  crimson, 
appeared  amongst  both  the  intercrossed  and  self- 
fertilised  plants.  It  prevailed  in  all  the  later  self- 
fertilised  generations  to  the  exclusion  of  every  other 
variety,  and  transmitted  its  characters  faithfully,  but 
disappeared  from  the  intercrossed  plants,  owing  no 
doubt  to  their  characters  being  repeatedly  blended  by 
crossing.  The  self  fertilised  plants  belonging  to  this 
variety  were  not  only  taller,  but  more  fertile  than  the 
intercrossed  plants  ;  though  these  latter  in  the  earlier 
generations  were  much  taller  and  more  fertile  than  the 
self-fertilised  plants.  Thus  in  the  fifth  generation  the 
self-fertilised  plants  were  to  the  intercrossed  in  height 
as  126  to  100.  In  the  sixth  generation  they  were 
likewise  much  taller  and  finer  plants,  but  were  not 
actually  measured ;  they  produced  capsules  compared 
with  those  on  the  intercrossed  plants,  in  number,  as  147 
to  100 ;  and  the  self-fertilised  capsules  contained  a 
greater  number  of  seeds.  In  the  seventh  generation 
the  self-fertilised  plants  were  to  the  crossed  in  height 
as  137  to  100 ;  and  twenty  flowers  on  these  self-fer- 
tilised plants  fertilised  with  their  own  pollen  yielded 
nineteen  very  fine  capsules, — a  degree  of  self-fertility 
which  I  have  not  seen  equalled  in  any  other  case.  This 
variety  seems  to  have  become  specially  adapted  to  profit 
in  every  way  by  self-fertilisation,  although  this  process 
was  so  injurious  to  the  parent-plants  during  the  first 


Chai\  IX.  SELF-FEKTTLE   VAEIETIES.  349 

four  generations.  It  should  however  be  remembered 
that  seedlings  raised  from  this  variety,  when  crossed  by 
a  fresh  stock,  were  wonderfully  superior  in  height  and 
fertility  to  the  self-fertilised  plants  of  the  corresponding 
generation. 

Secondly,  in  the  sixth  self-fertilised  generation  of 
Ipomoea  a  single  plant  named  the  Hero  appeared,  which 
exceeded  by  a  little  in  height  its  intercrossed  opponent, 
— a  case  which  had  not  occurred  in  any  previous 
generation.  Hero  transmitted  the  peculiar  colour  of 
its  flowers,  as  well  as  its  increased  tallness  and  a  high 
degree  of  self-fertility,  to  its  children,  grandchildren, 
and  great-grandchildren.  The  self-fertilised  children 
of  Hero  were  in  height  to  other  self-fertilised  plants 
of  the  same  stock  as  100  to  85.  Ten  self-fertilised 
capsules  produced  by  the  grandchildren  contained  on 
an  average  5  •  2  seeds ;  and  this  is  a  higher  average 
than  was  yielded  in  any  other  generation  by  the 
capsules  of  self-fertilised  flowers.  The  great-grand- 
children of  Hero  derived  from  a  cross  with  a  fresh 
stock  were  so  unhealthy,  from  having  been  grown  at 
an  unfavourable  season,  that  their  average  height  in 
comparison  with  that  of  the  self-fertilised  plants 
cannot  be  judged  of  with  any  safety ;  but  it  did  not 
appear  that  they  had  profited  even  by  a  cross  of  this 
kind. 

Thirdly,  the  plants  of  Nicotiana  on  which  I  experi- 
mented appear  to  come  under  the  present  class  of 
cases ;  for  they  varied  in  their  sexual  constitution 
and  were  more  or  less  highly  self-fertile.  They 
were  probably  the  offspring  of  plants  which  had  been 
spontaneously  self-fertilised  under  glass  for  several 
generations  in  this  country.  The  flowers  on  the 
parent-plants  which  were  first  fertilised  by  me  with  their 
own  pollen  yielded  half  again  as  many  seeds  as  did 


350  SELF-FERTILE   VARIETIES.  Ckap.  IX. 

those  which  were  crossed ;  and  the  seedlings  raised 
from  these  self-fertilised  seeds  exceeded  in  height 
those  raised  from  the  crossed  seeds  to  an  extraordinary 
degree.  In  the  second  and  third  generations,  although 
the  self-fertilised  plants  did  not  exceed  the  crossed  in 
height,  yet  their  self-fertilised  flowers  yielded  on  two 
occasions  considerably  more  seeds  than  the  crossed 
flowers,  even  than  those  which  were  crossed  with  pollen 
from  a  distinct  stock  or  variety. 

Lastly,  as  certain  individual  plants  of  Reseda  odorata 
and  lutea  are  incomparably  more  self-fertile  than  other 
individuals,  the  former  might  be  included  under  the 
present  heading  of  the  appearance  of  new  and  highly 
self-fertile  varieties.  But  in  this  case  we  should  have 
to  look  at  these  two  species  as  normally  self-sterile  ; 
and  this,  judging  by  my  experience,  appears  to  be  the 
correct  view. 

We  may  therefore  conclude  from  the  facts  now  given, 
that  varieties  sometimes  arise  which  when  self-fer- 
tilised possess  an  increased  power  of  producing  seeds 
and  of  growing  to  a  greater  height,  than  the  inter- 
crossed or  self-fertilised  plants  of  the  corresponding 
generation — all  the  plants  being  of  course  subjected 
to  the  same  conditions.  The  appearance  of  such 
varieties  is  interesting,  as  it  bears  on  the  existence 
under  nature  of  plants  which  regularly  fertilise  them- 
selves, such  as  Ophrys  apifera  and  a  few  other  orchids, 
or  as  Leersia  oryzoides,  which  produces  an  abundance 
of  cleistogene  flowers,  but  most  rarely  flowers  capable 
of  cross -fertilisation. 

Some  observations  made  on  other  plants  lead  me 
to  suspect  that  self-fertilisation  is  in  some  respects 
beneficial ;  although  the  benefit  thus  derived  is  as  a 
rule  very  small  compared  with  that  from  a  cross  with 
a  distinct  plant.    Thus  we  have  seen  in  the  last  chapter 


Chap.  IX  SELF-FERTILE  VARIETIES.  351 

that  seedlings  of  Ipomoea  and  Mimulus  raised  from 
flowers  fertilised  with  their  own  pollen,  which  is  the 
strictest  possible  form  of  self- fertilisation,  were  superior 
in  height,  weight,  and  in  early  flowering  to  the  seedlings 
raised  from  flowers  crossed  with  pollen  from  other  flowers 
on  the  same  plant ;  and  this  superiority  apparently  was 
too  strongly  marked  to  be  accidental.  Again,  the  cul- 
tivated varieties  of  the  common  pea  are  highly  self- 
fertile,  although  they  have  been  self-fertilised  for  many 
generations ;  and  they  exceeded  in  height  seedlings 
from  a  cross  between  two  plants  belonging  to  the  same 
variety  in  the  ratio  of  115  to  100  ;  but  then  only  four 
pairs  of  plants  were  measured  and  compared.  The 
self-fertility  of  Primula  veris  increased  after  several 
generations  of  illegitimate  fertilisation,  which  is  a 
process  closely  analogous  to  self-fertilisation,  but  only 
as  long  as  the  plants  were  cultivated  under  the  same 
favourable  conditions.  I  have  also  elsewhere  shown* 
that  with  Primula  veris  and  sinensis,  equal- styled 
varieties  occasionally  appear  which  possess  the  sexual 
organs  of  the  two  forms  combined  in  the  same  flower. 
Consequently  they  fertilise  themselves  in  a  legitimate 
manner  and  are  highly  self-fertile  ;  but  the  remarkable 
fact  is  that  they  are  rather  more  fertile  than  ordinary 
plants  of  the  same  species  legitimately  fertilised  by 
pollen  from  a  distinct  individual.  Formerly  it  appeared 
to  me  probable,  that  the  increased  fertility  of  these 
dimorphic  plants  might  be  accounted  for  by  the  stigma 
lying  so  close  to  the  anthers  that  it  was  impregnated  at 
the  most  favourable  age  and  time  of  the  day ;  but  this 
explanation  is  not  applicable  to  the  above  given  cases, 
in  which  the  flowers  were  artificially  fertilised  with 
their  own  pollen. 


*  '  Journal  Linn.  Soc.  Bot.'  vol.  x.  1867,  pp.  417,  419. 
16 


352  WEIGHT  AND   GEEMINATION   OF         Chap.  IX 

Considering  the  facts  now  adduced,  including  the 
appearance  of  those  varieties  which  are  more  fertile 
and  taller  than  their  parents  and  than  the  intercrossed 
plants  of  the  corresponding  generation,  it  is  difficult 
to  avoid  the  suspicion  that  self-fertilisation  is  in  some 
respects  advantageous;  though  if  this  be  really  the 
case,  any  such  advantage  is  as  a  rule  quite  insignifi- 
cant compared  with  that  from  a  cross  with  a  distinct 
plant,  and  especially  with  one  of  a  fresh  stock.  Should 
this  suspicion  be  hereafter  verified,  it  would  throw 
light,  as  we  shall  see  in  the  next  chapter,  on  the  exist- 
ence of  plants  bearing  small  and  inconspicuous  flowers 
which  are  rarely  visited  by  insects,  and  therefore  are 
rarely  intercrossed. 

Relative  Weight  and  Period  of  Germination  of  Seeds 
from  crossed  and  self-fertilised  Flowers. — An  equal 
number  of  seeds  from  flowers  fertilised  with  pollen  from 
another  plant,  and  from  flowers  fertilised  with  their  own 
pollen,  were  weighed,  but  only  in  sixteen  cases.  Their 
relative  weights  are  given  in  the  following  list ;  that 
of  the  seeds  from  the  crossed  flowers  being  taken  as  100. 


Ipomoea  purpurea  (parent  plants) 
„  „  (third  generation). 

Salvia  coccinea 

Brassica  oleracea 

Iberis  umbellata  (second  generation) 
Delphinium  consolida       .... 

Hibiscus  africanus 

Tropseolum  minus 

Lathyrus  odoratus  (about)     .      . 
Sarothamnus  scoparius     .... 

Specularia  speculum 

Nemophila  insignis 

Borago  officinalis 

Cyclamen  persicum  (about)   . 
Fagopyrum  esculentum    .... 
Canna  vvarscewiczi  (three  generations) 


100  to  127 

„  „   87 

„  „  100 

„  „  103 

„  „  136 

»  „   45 

„  „  105 

„     »  I15 

„  „  100 

„  „   88 

„  „   86 

„  „  105 

»  „     m 

„  „   50 

„  „   82 

„  „  102 

It  is  remarkable  that  in  ten  out  of  these  sixteen 


Chap.  IX.      CROSSED   AND   SELF-FERTILISED   SEEDS.      353 

cases  the  self-fertilised  seeds  were  either  superior  or 
equal  to  the  crossed  in  weight ;  nevertheless,  in  six  out 
of  the  ten  cases  (viz.,  with  Iponioea,  Salvia,  Brassica, 
Tropasolum,  Lathyrus,  and  Nemophila)  the  plants 
raised  from  these  self-fertilised  seeds  were  very  inferior 
in  height  and  in  other  respects  to  those  raised  from  the 
crossed  seeds.  The  superiority  in  weight  of  the  self- 
fertilised  seeds  in  at  least  six  out  of  the  ten  cases, 
namely,  with  Brassica,  Hibiscus,  Tropgeolum,  Nemophila, 
Borago,  and  Canna,  may  be  accounted  for  in  part  by 
the  self- fertilised  capsules  containing  fewer  seeds  ;  for 
when  a  capsule  contains  only  a  few  seeds,  these  will  be 
apt  to  be  better  nourished,  so  as  to  be  heavier,  than 
when  many  are  contained  in  the  same  capsule.  It 
should,  however,  be  observed  that  in  some  of  the  above 
cases,  in  which  the  crossed  seeds  were  the  heaviest,  as 
with  Sarotharanus  and  Cyclamen,  the  crossed  capsules 
contained  a  larger  number  of  seeds.  Whatever  may  be 
the  explanation  of  the  self-fertilised  seeds  being  often 
the  heaviest,  it  is  remarkable  in  the  case  of  Brassica, 
Tropseolum,  Nemophila,  and  of  the  first  generation  of 
Iponioea,  that  the  seedlings  raised  from  them  were 
inferior  in  height  and  in  other  respects  to  the  seed- 
lings raised  from  the  crossed  seeds.  This  fact  shows 
how  superior  in  constitutional  vigour  the  crossed  seed- 
lings must  have  been,  for  it  cannot  be  doubted  that 
heavy  and  fine  seeds  tend  to  yield  the  finest  plants. 
Mr.  Galton  has  shown  that  this  holds  good  with  Lathyrus 
odoratus ;  as  has  Mr.  A.  J.  Wilson  with  the  Swedish 
turnip,  Brassica  campestris  ruta  hag  a.  Mr.  Wilson 
separated  the  largest  and  smallest  seeds  of  this  latter 
plant,  the  ratio  between  the  weights  of  the  two  lots 
being  as  100  to  59,  and  he  found  that  the  seedlings 
"  from  the  larger  seeds  took  the  lead  and  maintained 
their  superiority  to  the  last,  both  in  height  and  thick- 


354  WEIGHT  AND   GEEMINATION  OF         Chap.  IX, 

ness  of  stem."*  Nor  can  this  difference  in  the  growth 
of  the  seedling  turnips  be  attributed  to  the  heaviei 
seeds  having  been  of  crossed,  and  the  lighter  of  self- 
fertilised  origin,  for  it  is  known  that  plants  belonging 
to  this  genus  are  habitually  intercrossed  by  insects. 

With  respect  to  the  relative  period  of  germination  of 
crossed  and  self-fertilised  seeds,  a  record  was  kept  in 
only  twenty-one  cases ;  and  the  results  are  very  per- 
plexing. Neglecting  one  case  in  which  the  two  lots 
germinated  simultaneously,  in  ten  cases  or  exactly  one- 
half  many  of  the  self-fertilised  seeds  germinated  before 
the  crossed,  and  in  the  other  half  many  of  the  crossed 
before  the  self- fertilised.  In  four  out  of  these  twenty 
cases,  seeds  derived  from  a  cross  with  a  fresh  stock 
were  compared  with  self-fertilised  seeds  from  one  of  the 
later  self-fertilised  generations  ;  and  here  again  in  half 
the  cases  the  crossed  seeds,  and  in  the  other  half  the 
self-fertilised  seeds,  germinated  first.  Yet  the  seedlings 
of  Mimulus  raised  from  such  self-fertilised  seeds  were 
inferior  in  all  respects  to  the  crossed  seedlings,  and  in 
the  case  of  Eschscholtzia  they  were  inferior  in  fertility. 
Unfortunately  the  relative  weight  of  the  two  lots  of 
seeds  was  ascertained  in  only  a  few  instances  in  which 
their  germination  was  observed  ;  but  with  Ipomoea  and 
I  believe  with  some  of  the  other  species,  the  relative 
lightness  of  the  self-fertilised  seeds  apparently  deter- 


*  '  Gardeners'  Chronicle,'  1867,  by  long-continued  selection,  may 

p.  107.     Loiseleur-Deslongehamp  have  given  to  the  grains  of  the 

('  Les  Ce're'ales,'  1842,  pp.  208-219)  cereals  a  greater  amount  of  starch 

was  led  by  his   observations  to  or  other  matter,  than  the  seed- 

the  extraordinary  conclusion  that  lings  can  utilise  for  their  growth, 

the  smaller  grains  of  cereals  pro-  There    can    be    little    doubt,   as 

duce  as  fine  plants  as  the  large.  Humboldt    long    ago    remarked, 

This  conclusion  is,  however,  con-  that  the  grains  of  cereals  have 

tradicted  by  Major  Hallet's  great  been  rendered  attractive  to  birds 

success  in   improving  wheat  by  in  a  degree  which  is  highly  in- 

the  selection  of  the  finest  grains.  juiious  to  the  species. 
It  is  possible,  however,  that  man, 


Chap.  IX.      CKOSSED   AND    SELF-FEKTILISED   SEEDS.      355 

mined  their  early  germination,  probably  owing  to  the 
smaller  mass  being  favourable  to  the  more  rapid  com- 
pletion of  the  chemical  and  morphological  changes 
necessary  for  germination.  On  the  other  hand,  Mr. 
Galton  gave  me  seeds  (no  doubt  all  self-fertilised)  of 
Lathyrus  odoratus,  which  were  divided  into  two  lots  of 
heavier  and  lighter  seeds ;  and  several  of  the  former 
germinated  first.  It  is  evident  that  many  more  observa- 
tions are  necessary  before  anything  can  be  decided 
with  respect  to  the  relative  period  of  germination  of 
crossed  and  self-fertilised  seeds. 


356  MEANS   OF   FERTILISATION.  Chap.  X. 


CHAPTEE  X. 

Means  of  Fertilisation. 

Sterility  and  fertility  of  plants  when  insects  are  excluded — The  means 
by  which  flowers  are  cross-fertilised — Structures  favourable  to  self- 
fertilisation — Relation  between  the  structure  and  conspicuousneas 
of  flowers,  the  visits  of  insects,  and  the  advantages  of  cross-fertilisa- 
tion—  The  means  by  which  flowers  are  fertilised  with  pollen 
from  a  distinct  plant — Greater  fertilising  power  of  such  pollen 
— Anemophilous  t-pecies — Conversion  of  anemophilous  species  into 
entomophilous — Origin  of  nectar — Anemophilous  plants  generally 
have  their  sexes  separated  — Conversion  of  diclinous  into  herma- 
phrodite flowers — Trees  often  have  their  sexes  separated. 

In  the  introductory  chapter  I  briefly  specified  the 
various  means  by  which  cross-fertilisation  is  favoured 
or  ensured,  namely,  the  separation  of  the  sexes, — the 
maturity  of  the  male  and  female  sexual  elements  at 
different  periods,  —  the  heterostyled  or  dimorphic 
and  trimorphic  condition  of  certain  plants,  —  many 
mechanical  contrivances, — the  more  or  less  complete 
inefficiency  of  a  flower's  own  pollen  on  the  stigma, — and 
the  prepotency  of  pollen  from  any  other  individual 
over  that  from  the  same  plant.  Some  of  these  points 
require  further  consideration ;  but  for  full  details  I 
must  refer  the  reader  to  the  several  excellent  works 
mentioned  in  the  introduction.  I  will  in  the  first  place 
give  two  lists  :  the  first,  of  plants  which  are  either  quite 
sterile  or  produce  less  than  about  half  the  full  com- 
plement of  seeds,  when  insects  are  excluded ;  and  a 
second  list  of  plants  which,  when  thus  treated,  are  fully 
fertile  or  produce  at  least  half   the  full  complement 


Chap.  X.  MEANS   OF   FEETILISATIOK.  357 

of  seeds.  These  lists  have  been  compiled  from  the 
several  previous  tables,  with  some  additional  cases  from 
my  own  observations  and  those  of  others.  The  species 
are  arranged  nearly  in  the  order  followed  by  Lindley 
in  his  'Vegetable  Kingdom.'  The  reader  should 
observe  that  the  sterility  or  fertility  of  the  plants  in 
these  two  lists  depends  on  two  wholly  distinct  causes ; 
namely,  the  absence  or  presence  of  the  proper  means 
by  which  pollen  is  applied  to  the  stigma,  and  its  less 
or  greater  efficiency  when  thus  applied.  As  it  is 
obvious  that  with  plants  in  which  the  sexes  are  separate, 
pollen  must  be  carried  by  some  means  from  flower  to 
flower,  such  species  are  excluded  from  the  lists ;  as 
are  likewise  dimorphic  and  trimorphic  plants,  in  which 
the  same  necessity  occurs  to  a  limited  extent.  Ex- 
perience has  proved  to  me  that,  independently  of  the 
exclusion  of  insects,  the  seed-bearing  power  of  a  plant 
is  not  lessened  by  covering  it  while  in  flower  under  a 
thin  net  supported  on  a  frame ;  and  this  might  indeed 
have  been  inferred  from  the  consideration  of  the  two 
following  lists,  as  they  include  a  considerable  number 
of  species  belonging  to  the  same  genera,  some  of  which 
are  quite  sterile  and  others  quite  fertile  when  protected 
by  a  net  from  the  access  of  insects. 

List  of  Plants  which,  when  Insects  are  excluded,  are  either 
quite  sterile,  or  produce,  as  far  as  I  could  judge,  less 
than  half  the  number  of  Seeds  produced  by  unpro- 
tected Plants. 

Passiflora  alata,  racemosa,  ccerulea,  edulis,  laurifolia,  and  some 
individuals  of  P.  quadrangula/ris  (Passifloraceas),  are  quite 
sterile  under  these  conditions :  see  '  Variation  of  Animals 
and  Plants  under  Domestication/  chap.  xvii.  2nd  edit.  vol.  ii. 
p.  118. 

Viola  canina  (Violficese). — Perfect  flowers  quite  sterile  unless 
fertilised  by  bees,  or  artificially  fertilised. 


858       PLANTS   STERILE  WITHOUT  INSECT- AID.      Chap.  X. 

V.  tricolor. — Sets  very  few  and  poor  capsules. 

Reseda  odorata  (Kesedacese). — Some  individuals  quite  sterile. 

B.  lutea. — Some  individuals  produce  very  few  and  poor  cap- 

sules. 

Abutilon  darwinii  (Malvaceae). —  Quite  sterile  in  Brazil :  see 
previous  discussion  on  self-sterile  plants. 

Nymphcea  (Nympbseaceae). — Professor  Caspary  informs  me  that 
some  of  the  species  are  quite  sterile  if  insects  are  excluded. 

Euryale  amazonica  (Nyrnphseacese). — Mr.  J.  Smith,  of  Kew,  in- 
forms me  that  capsules  from  flowers  left  to  themselves,  and 
probably  not  visited  by  insects,  contained  from  eight  to  fif- 
teen seeds ;  those  from  flowers  artificially  fertilised  with 
pollen  from  other  flowers  on  the  same  plant  contained  from 
fifteen  to  thirty  seeds  ;  and  that  two  flowers  fertilised  with 
pollen  brought  from  another  plant  at  Chatsworth  contained 
respectively  sixty  and  seventy-five  seeds.  I  have  given 
these  statements  because  Professor  Caspary  advances  this 
plant  as  a  case  opposed  to  the  doctrine  of  the  necessity  or 
advantage  of  cross-fertilisation:  see  Sitzungsberichte  der 
Phys.-okon.  Gesell.  zu  Konigsberg,  B.  vi.  p.  20. 

Delphinium  consolida  (Kanunculacese). — Produces  many  capsules, 
but  these  contain  only  about  half  the  number  of  seeds  com- 
pared with  capsules  from  flowers  naturally  fertilised  by 
bees. 

Eschscholtzia  californica  (Papaveracese). — Brazilian  plants  quite 
sterile :  English  plants  produce  a  few  capsules. 

Papnver  vagum  (Papaveracese). — In  tbe  early  part  of  the  summer 
produced  very  few  capsules,  and  these  contained  very  few 
seeds. 

P.  alpinum. — H.  Hoffmann  (f  Speciesfrage,'  1875,  p.  47)  states 
tbat  this  species  produced  seeds  capable  of  germination  only 
on  one  occasion. 

Corydalis  cava  (Fumariacese). — Sterile :  see  the  previous  discus- 
sion on  self-sterile  plants. 

C.  solida. — I  had  a  single  plant  in  my  garden  (1863),  and  saw 

many  hive-bees  sucking  the  flowers,  but  not  a  single  seed 
was  produced.  I  was  much  surprised  at  this  fact,  as  Pro- 
fessor Hildebrand's  discovery  that  0.  cava  is  sterile  with  its 
own  pollen  had  not  then  been  made.  He  likewise  concludes 
from  the  few  experiments  which  he  made  on  the  present 
species  that  it  is  self-sterile.  The  two  foregoing  cases  are 
interesting,  because   botanists  formerly  thought    (see,  for 


Chap.  X.      PLANTS   STEEILE   WITHOUT   INSECT-AID.       359 

instance,  Lecoq,  '  De  la  Fecondation  et  de  l'Hybridation/ 
1845,  p.  61,  and  Lindley,  'Vegetable  Kingdom/  1853,  p.  -136) 
that  all  the  species  of  the  Furnariacese  were  specially  adapted, 
for  self-fertilisation. 

0.  lutea. — A  covered-up  plant  produced  (1861)  exactly  half  as 
many  capsules  as  an  exposed  plant  of  the  same  size  grow- 
ing close  alongside.  When  humble-bees  visit  the  flowers 
(and  I  repeatedly  saw  them  thus  acting)  the  lower  petals 
suddenly  spring  downwards  and  the  pistil  upwards;  this 
is  due  to  the  elasticity  of  the  parts,  which  takes  effect,  as 
soon  as  the  coherent  edges  of  the  hood  are  separated  by  the 
entrance  of  an  insect.  Unless  insects  visit  the  flowers  the 
parts  do  not  move.  Nevertheless,  many  of  the  flowers  on 
the  plants  which  I  had  protected  produced  capsules,  not- 
withstanding that  their  petals  and  pistils  still  retained  their 
original  position ;  and  I  found  to  my  surprise  that  these 
capsules  contained  more  seeds  than  those  from  flowers,  the 
petals  of  which  had  been  artificially  separated  and  allowed 
to  spring  apart.  Thus,  nine  capsules  produced  by  undis- 
turbed flowers  contained  fifty-three  seeds ;  whilst  nine  cap- 
sules from  flowers,  the  petals  of  which  had  been  artificially 
separated,  contained  only  thirty-two  seeds.  But  we  should 
remember  that  if  bees  had  been  permitted  to  visit  these 
flowers,  they  would  have  visited  them  at  the  best  time  for 
fertilisation.  The  flowers,  the  petals  of  which  had  been 
artificially  separated,  set  their  capsules  before  those  which 
were  left  undisturbed  under  the  net.  To  show  with  what 
certainty  the  flowers  are  visited  by  bees,  I  may  add  that 
on  one  occasion  all  the  flowers  on  some  unprotected  plants 
wer!e  examined,  and  every  single  one  had  its  petals  sepa- 
rated; and,  on  a  second  occasion,  forty-one  out  of  forty- 
three  flowers  were  in  this  state.  Hildebrand  states  (Pring. 
Jahr.  f.  wiss.  Botanik,  B.  vii.,  p.  450)  that  the  mechanism 
of  the  parts  in  this  species  is  nearly  the  same  as  in  G.  ochro- 
leuca,  which  he  has  fully  described. 

Hypecoum  grandiflorum  (Fumariacese). — Highly  self-sterile  (Hil- 
debrand, ibid.). 

Kalmia  latifolia  (Ericaceae). — Mr.  W.  J.  Beal  says  ('  American 
Naturalist,'  1867)  that  flowers  protected  from  insects  wither 
and  drop  off,  with  "  most  of  the  anthers  still  remaining  in 
the  pockets." 

Pelargonium  zonale  (Geraniaceae).— Almost  sterile;    one  plant 


360       PLANTS   STERILE   WITHOUT   INSECT-AID.      Chap.  X. 

produced  two  fruits.    It  is  probable  that  different  yarieties 
would  differ  in  this  respect,  as  some  are  only  feebly  dicho- 
gamous. 
Dianthus    caryopliyllus    (Caryophyllacese). — Produces  very  few 

capsules,  which  contain  any  good  seeds. 
Phaseolus    multiflorus   (Leguminosse). —  Plants  protected    from 
insects  produced  on  two  occasions  about  one-third  and  one- 
eighth  of  the  full  number  of   seeds:  see  my  article  in 
'Gardeners'  Chronicle,'  1857,  p.  225,  and  1858,  p.  828;  also 
'Annals  and  Mag.  of  Natural  History,'  3rd  series,  vol.  ii. 
1858,  p.  462.    Dr.  Ogle  ('  Pop.  Science  Beview/  1870,  p.  168) 
found  that  a  plant  was  quite  sterile  when  covered  up.     The 
flowers  are  not  visited  by  insects  in  Nicaragua,  and,  accord- 
ing to  Mr.  Belt,  the  species  is  there  quite  sterile :   '  The 
Naturalist  in  Nicaragua,'  p.  70. 
Viciafaba  (Leguminosse). — Seventeen  covered-up  plants  yielded 
40  beans,  whilst  seventeen    plants  left  unprotected  and 
growing  close  alongside  produced  135  beans ;  these  latter 
plants  were,  therefore,  between  three  and  four  times  more 
fertile  than  the  protected  plants :  see  '  Gardeners'  Chronicle  ' 
for  fuller  details,  1858,  p.  828. 
Erythrina  (sp.  ?)  (Leguminosse). — Sir  W.  MacArthur  informed 
me  that  in  New  South  Wales  the  flowers  do  not  set,  unless 
the  petals  are  moved  in  the  same  manner  as  is  done  by 
insects. 
Lathyrus  glandiflorus  (LeguminoSce). — Is  in  this  country  more  or 
less  sterile.    It  never  sets  pods  unless  the  flowers  are  visited 
by  humble-bees  (and  this  happens  only  rarely),  or  unless 
they  are  artificially  fertilised :  see  my  article  in  '  Gardeners' 
Chronicle/  1858,  p.  828. 
Sarothamnus  scoparius  (Leguminosse). — Extremely  sterile  when 
the  flowers  are  neither  visited  by  bees,  nor  disturbed  by 
being  beaten  by  the  wind  against  the  surrounding  net. 
Melilotus  officinalis  (Leguminosse). — An  unprotected  plant  visited 
by  bees  produced  at  least  thirty  times  more  seeds  than  a 
protected  one.     On  this  latter  plant  many  scores  of  racemes 
did  not  produce  a  single  pod;  several  racemes  produced 
each  one  or  two  pods ;  five  produced  three ;  six  produced 
four ;  and  one  produced  six  pods.   On  the  unprotected  plant 
each  of  several  racemes  produced  fifteen  pods ;  nine  pro- 
duced  between    sixteen    and    twenty-two    pods,  and    one 
produced  thirty  pods. 


Chap.  X.      PLANTS   STEKILE   WITHOUT   INSECT-AID.       361 

Lotus  corniculatus  (Leguminosae). — Several  covered-up  plants 
produced  only  two  empty  pods,  and  not  a  single  good  seed. 

Trifolium  repens  (Leguminosae). — Several  plants  were  protected 
from  insects,  and  the  seeds  from  ten  flower-heads  on  these 
plants,  and  from  ten  heads  on  other  plants  growing  outside 
the  net  (which  I  saw  visited  by  bees),  were  counted  ;  and 
the  seeds  from  the  latter  plants  were  very  nearly  ten  times 
as  numerous  as  those  from  the  protected  plants.  The  ex- 
periment was  repeated  on  the  following  year;  and  twenty 
protected  heads  now  yielded  only  a  single  aborted  seed, 
whilst  twenty  heads  on  the  plants  outside  the  net  (which  I 
saw  visited  by  bees)  yielded  2290  seeds,  as  calculated  by 
weighing  all  the  seed,  and  counting  the  number  in  a  weight 
of  two  grains. 

T.  pratense. — One  hundred  flower-heads  on  plants  protected  by 
a  net  did  not  produce  a  single  seed,  whilst  100  heads  on 
plants  growing  outside,  which  were  visited  by  bees,  yielded 
68  grains  weight  of  seeds ;  and  as  eighty  seeds  weighed  two 
grains,  the  100  heads  must  have  yielded  2,720  seeds.  I  have 
often  watched  this  plant,  and  have  never  seen  hive-bees 
sucking  the  flowers,  except  from  the  outside  through  holes 
bitten  by  humble-bees,  or  deep  down  between  the  flowers,  as 
if  in  search  of  some  secretion  from  the  calyx,  almost  in  the 
same  manner  as  described  by  Mr.  Farrer,  in  the  case  of 
Coronilla  ('Nature,'  1874,  July  2,  p.  169).  I  must,  how- 
ever, except  one  occasion,  when  an  adjoining  field  of  sainfoin 
(Hedysarum  onobrychis)  had  just  been  cut  down,  and  when 
the  bees  seemed  driven  to  desperation.  On  this  occasion 
most  of  the  flowers  of  the  clover  were  somewhat  withered, 
and  contained  an  extraordinary  quantity  of  ne<ctar,  which 
the  bees  were  able  to  suck.  An  experienced  apiarian, 
Mr.  Miner,  says  that  in  the  United  States  hive-bees  never 
suck  the  red  clover ;  and  Mr.  E.  Colgate  informs  me  that 
he  has  observed  the  same  fact  in  New  Zealand  after  the 
introduction  of  the  hive-bee  into  that  island.  On  the  other 
hand,  H.  Miiller  ('  BefruchtuEg,'  p.  224)  has  often  seen  hive- 
bees  visiting  this  plant  in  Germany,  for  the  sake  both  of 
pollen  and  nectar,  which  latter  they  obtained  by  breaking 
apart  the  petals.  It  is  at  least  certain  that  humble-bees  are 
the  chief  fertilisers  of  the  common  red  clover. 

I  incarnatum. — The  flower-heads  containing  ripe  seeds,  on  some 
covered  and  uncovered  plants,  appeared  equally  fine,  but 


362       PLANTS   STEEILE   WITHOUT  INSECT- AID.      Chap.  X. 

this  was  a  false  appearance ;  60  heads  on  the  latter  yielded 
349  grains  weight  of  seeds,  whereas  60  on  the  covered-up 
plants  yielded  only  63  grains,  and  many  of  the  seeds  in  the 
latter  lot  were  poor  and  aborted.  Therefore  the  flowers 
which  were  visited  by  bees  produced  between  five  and  six 
times  as  many  seeds  as  those  which  were  protected.  The 
covered-np  plants  not  having  been  much  exhausted  by  seed- 
bearing,  bore  a  second  considerable  crop  of  flower-stems, 
whilst  the  exposed  plants  did  not  do  so. 

Cytisus  laburnum  (Leguminosae). — Seven  flower-racemes  ready  to 
expand  were  enclosed  in  a  large  bag  made  of  net,  and  they 
did  not  seem  in  the  least  injured  by  this  treatment.  Only 
three  of  them  produced  any  pods,  each  a  single  one ;  and 
these  three  pods  contained  one,  four,  and  five  seeds.  So 
that  only  a  single  pod  from  the  seven  racemes  included  a 
fair  complement  of  seeds. 

Cuphea  purpurea  (Lythraceae). — Produced  no  seeds.  Other  flowers 
on  the  same  plant  artificially  fertilised  under  the  net  yielded 
seeds. 

Vinca  major  (Apocynaceae). — Is  generally  quite  sterile,  but  some- 
times sets  seeds  when  artificially  cross-fertilised :  see  my 
notice, '  Gardeners'  Chronicle,'  1861,  p.  552. 

V.  rosea. — Behaves  in  the  same  manner  as  the  last  species: 
'  Gardeners'  Chronicle/  1861,  pp.  699,  736,  831. 

Tabernazmonlana  echinata  (Apocynaceae). — Quite  sterile. 

Petunia  violacea  (Solanaceae). — Quite  sterile,  as  far  as  I  have 
observed. 

Solanum  tuberosum  (Solanaceae). — Tinzmann  says  ('Gardeners' 
Chronicle/  1846,  p.  183)  that  some  varieties  are  quite  sterile 
unless  fertilised  by  pollen  from  another  variety. 

Primula  scotica  (Primulaceae). — A  non-dimorphic  species,  which 
is  fertile  with  its  own  pollen,  but  is  extremely  sterile  if 
insects  are  excluded.  J.  Scott,  in  '  Journal  Linn.  Soc.  Bot. 
vol.  viii.  1864,  p.  119. 

Cortusa  matthioli  (Primulaceae). — Protected  plants  completely 
sterile;  artificially  self-fertilised  flowers  perfectly  fertile. 
J.  Scott,  ibid.  p.  84. 

Cyclamen  persicum  (Primulacese). — During  one  season  several 
covered-up  plants  did  not  produce  a  single  seed. 

Borago  officinalis  (Boraginaceae). — Protected  plants  produced 
about  half  as  many  seeds  as  the  unprotected. 

Salvia  tenori  (Labiatse). — Quite  sterile ;  but  two  or  three  flowers 


Chap.  X.      PLANTS   STERILE   WITHOUT   INSECT-AID.       363 

on  the  summits  of  three  of  the  spikes/  which  touched  the 
net  when  the  wind  blew,  produced  a  few  seeds.  This 
sterility  was  not  due  to  the  injurious  effects  of  the  net,  for  I 
fertilised  five  flowers  with  pollen  from  an  adjoining  plant, 
and  these  all  yielded  fine  seeds.  I  removed  the  net,  whilst 
one  little  branch  still  bore  a  few  not  completely  faded 
flowers,  and  these  were  visited  by  bees  and  yielded  seeds. 

S.  coccinea. — Some  covered-up  plants  produced  a  good  many 
fruits,  but  not,  I  think,  half  as  many  as  did  the  uncovered 
plants ;  twenty-eight  of  the  fruits  spontaneously  produced 
by  the  protected  plant  contained  on  an  average  only  1"  45 
seeds,  whilst  some  artificially  self- fertilised  fruits  on  the 
same  plant  contained  more  than  twice  as  many,  viz.,  3*3 
seeds. 

Bignonia  (unnamed  species)  (Bignoniacese).—  Quite  sterile:  see 
my  account  of  self-sterile  plants. 

Digitalis  purpurea  (Scrophulariacese). — Extremely  sterile,  only  a 
few  poor  capsules  being  produced. 

Linaria  vulgaris  (Scrophulariacese). — Extremely  sterile. 

Antirrhinum  majus,  red  var.  (Scrophulariaccas). — Fifty  pods 
gathered  from  a  large  plant  under  a  net  contained  9*8  grains 
weight  of  seeds ;  but  many  (unfortunately  not  counted)  of 
the  fifty  pods  contained  no  seeds.  Fifty  pods  on  a  plant 
fully  exposed  to  the  visits  of  humble-bees  contained  '23  *  1 
grains  weight  of  seed,  that  is,  more  than  twice  the  weight ; 
but  in  this  case  again,  several  of  the  fifty  pods  contained  no 
seeds. 

A.  majus  (white  var.,  with  a  pink  mouth  to  the  corolla). — 
Fifty  pods,  of  which  only  a  very  few  were  empty,  on  a 
covered-up  plant  contained  20  grains  weight  of  seed;  so 
that  this  variety  seems  to  be  much  more  self-fertile  than 
the  previous  one.  With  Dr.  W.  Ogle  ('Pop.  Science 
Review,'  Jan.  1870,  p.  52)  a  plant  of  this  species  was  much 
more  sterile  when  protected  from  insects  than  with  me,  for 
it  produced  only  two  small  capsules.  As  showing  the 
efficiency  of  bees,  I  may  add  that  Mr.  Crocker  castrated  some 
young  flowers  and  left  them  uncovered ;  and  these  produced 
as  many  seeds  as  the  unmutilated  flowers. 

A.  majus  (peloric  var.). — This  variety  is  quite  fertile  when  arti- 
ficially fertilised  with  its  own  pollen,  but  is  utterly  sterile 
when  left  to  itself  and  uncovered,  as  humble-bees  cannot 
crawl  into  the  narrow  tubular  flowers. 


364       PLANTS  STEEILE   WITHOUT  INSECT-AID.      Chap.  X. 

Verhascum phceniceum  (Scrophulariaceae). — Quite  sterile ) See  ™y  sc' 

,-,      .  /~,    •,        ■      -i  >count  of  self- 

V.  nigrum. — Quite  sterile  .....  |  sterile  plants. 

Campanula  carpathica  (Lobeliaceae). — Quite  sterile. 

Lobelia  ramosa  (Lobeliaceae). — Quite  sterile. 

L.fulgens. — This  plant  is  never  visited  in  my  garden  by  bees, 
and  is  quite  sterile ;  but  in  a  nursery-garden  at  a  few  miles' 
distance  I  saw  humble-bees  visiting  the  flowers,  and  they 
produced  some  capsules. 

Isotoma  (a  white-flowered  var.)  (Lobeliacese). — Five  plants  left 
unprotected  in  my  greenhouse  produced  twenty-four  fine 
capsules,  containing  altogether  12*2  grains  weight  of  seed, 
and  thirteen  other  very  poor  capsules,  which  were  rejected. 
Five  plants  protected  from  insects,  but  otherwise  exposed 
to  the  same  conditions  as  the  above  plants,  produced  sixteen 
fine  capsules,  and  twenty  other  very  poor  and  rejected  ones. 
The  sixteen  fine  capsules  contained  seeds  by  weight  in  such 
proportion  that  twenty-four  would  have  yielded  4"  G6 
grains.  So  that  the  unprotected  plants  produced  nearly 
thrice  as  many  seeds  by  weight  as  the  protected  plants. 

Leschenaultia  formosa  (Goodeniaceae). — Quite  sterile.  My  experi- 
ments on  this  plant,  showing  the  necessity  of  insect  aid, 
are  given  in  the  '  Gardeners'  Chronicle,'  1871,  p.  1166. 

Senecio  cruentus  (Compositae). — Quite  sterile :  see  my  account  of 
self-sterile  plants. 

Eeterocentron  mexicanum  (Malastomaceae). — Quite  sterile ;  but 
this  species  and  the  following  members  of  the  group  pro- 
duce plenty  of  seed  when  artificially  self-fertilised. 

Ehexia  glandulosa  (Mslastoniaceae). — Set  spontaneously  only  two 
or  three  capsules. 

Centradeniafloribunda(M.ela,stom&ce3d). — During  some  years  pro- 
duced spontaneously  two  or  three  capsules,  sometimes 
none. 

Pleroma  (unnamed  species  from  Kew)  (Melastomaceae). — During 
some  years  produced  spontaneously  two  or  three  capsules, 
sometimes  none. 

Monochcetum  ensiferum  (Melastomaceae). — During  some  years  pro- 
duced spontaneously  two  or  three  capsules,  sometimes 
none. 

Hedychium  (unnamed  species)  (Marantacese). — Almost  self-sterile 
without  aid. 

Orchidece. — An  immense  proportion  of  the  species  sterile,  if 
insects  are  excluded. 


Chap.  X.     PLANTS   FEETILE   WITHOUT   INSECT-AID.       365 

List  of  Plants,  which  when  protected  from  Insects  are 
either  quite  Fertile,  or  yield  more  than  half  the  Number 
of  Seeds  produced  by  unprotected  Plants. 

Passiflora  gracilis  (Passifioracese). — Produces  many  fruits,  but 
these  contain  fewer  seeds  than  fruits  from  intercrossed  flowers. 

Brassica  oleracea  (Cruciferae).  —  Produces  many  capsules,  but 
these  generally  not  so  rich  in  seed  as  those  on  uncovered 
plants. 

Baphanus  sativus  (Cruciferge). — Half  of  a  large  branching  plant 
was  covered  by  a  net,  and  was  as  thickly  covered  with 
capsules  as  the  other  and  unprotected  half;  but  twenty  of 
the  capsules  on  the  latter  contained  on  an  average  3*5 
seeds,  whilst  twenty  of  the  protected  capsules  contained  only 
1"85  seeds,  that  is,  only  a  little  more  than  half  the  number. 
This  plant  might  perhaps  have  been  more  properly  included 
in  the  former  list. 

Iberis  umbettata  (Cruciferse). — Highly  fertile. 

1.  amara. — Highly  fertile. 

Beseda  odorata  and  lutea  (KesedaceaB). — 'Certain  individuals  com- 
pletely self-fertile. 

Euryaleferox  (Nymphseacese). — Professor  Caspary  informs  me  that 
this  plant  is  highly  self-fertile  when  insects  are  excluded.  He 
remarks  in  the  paper  before  referred  to,  that  his  plants  (as 
well  as  those  of  the  Victoria  regia)  produce  only  one  flower 
at  a  time ;  and  that  as  this  species  is  an  annual,  and  was 
introduced  in  1809,  it  must  have  been  self-fertilised  for  the 
last  fifty-six  generations ;  but  Dr.  Hooker  assures  me  that  to 
his  knowledge  it  has  been  repeatedly  introduced,  and  that  at 
Kew  the  same  plant  both  of  the  Euryale  and  of  the  Victoria 
produce  several  flowers  at  the  same  time. 

Nymphoza  (Nymphseacese). — Some  species,  as  I  am  informed  by 
Professor  Caspary,  are  quite  self-fertile  when  insects  are 
excluded. 

Adonis  aestivalis  (Ranunculacese). — Produces,  according  to  Pro- 
fessor H.  Hoffmann  ('  Speciesfrage,'  p.  11),  plenty  of  seeds 
when  protected  from  insects. 

Banunculus  acris  (Ranunculacese). — Produces  plenty  of  seeds 
under  a  net. 

Papaver  somniferum  (Papaveracese). — Thirty  capsules  from  un- 
covered plants  yielded  15  "6  grains  weight  of  seed,  and  thirty 
capsules  from  covered-up  plants,  growing  in  the  same  bed, 


366       PLANTS  FEETILE  WITHOUT  INSECT-AID.      Chap.  X. 

yielded  16 "5  grains  weight;  so  that  the  latter  plants  were 
more  productive  than  the  uncovered.  Professor  H.  Hoffmann 
('  Speciesfrage/  1875,  p.  53)  also  found  this  species  self-fertile 
when  protected  from  insects. 
P.  vagum. — Produced  late  in  the  summer  plenty  of  seeds,  which 
germinated  well. 

P.  argemonoides        .  .  .  .  \  According   to  Hildebrand    ('  Jahr- 

Glaucium  luteum  (Papaveracea,)         .     ^JS^i_gXft£2l 

Argemone  ochroleuca  (Papaveraceaa)    .  J   are  by  no  means  sterile. 

Adlumia  cirrhosa  (Fumariaceae). — Sets  an  abundance  of  capsules. 

Bypecoum  procumbens  (Fumariaceae).  Hildebrand  says  (idem), 
with  respect  to  protected  flowers,  that  "  eine  gute  Frucht- 
bildung  eintrete." 

Fumaria  officinalis  (Fumariacese). — Covered-up  and  unprotected 
plants  apparently  produced  an  equal  number  of  capsules, 
and  the  seeds  of  the  former  seemed  to  the  eye  equally  good. 
I  have  often  watched  this  plant,  and  so  has  Hildebrand,  and 
we  have  never  seen  an  insect  visit  the  flowers.  H.  Miiller 
has  likewise  been  struck  with  the  rarity  of  the  visits  of  insects 
to  it,  though  he  has  sometimes  seen  hive-bees  at  work. 
The  flowers  may  perhaps  be  visited  by  small  moths,  as  is 
probably  the  case  with  the  following  species. 

F.  capreolata. — Several  large  beds  of  this  plant  growing  wild 
were  watched  by  me  during  many  days,  but  the  flowers 
were  never  visited  by  any  insects,  though  a  humble-bee 
was  once  seen  closely  to  inspect  them.  Nevertheless,  as 
the  nectary  contains  much  nectar,  especially  in  the  evening, 
I  felt  convinced  that  they  were  visited,  probably  by  moths. 
The  petals  do  not  naturally  separate  or  open  in  the  least ; 
but  they  had  been  opened  by  some  means  in  a  certain  pro- 
portion of  the  flowers,  in  the  same  manner  as  follows  when 
a  thick  bristle  is  pushed  into  the  nectary ;  so  that  in  this 
respect  they  resemble  the  flowers  of  Gorydalis  lutea.  Thirty- 
four  heads,  each  including  many  flowers,  were  examined, 
and  twenty  of  them  had  from  one  to  four  flowers,  whilst 
fourteen  had  not  a  single  flower  thus  opened.  It  is  there- 
fore clear  that  some  of  the  flowers  had  been  visited  by 
insects,  while  the  majority  had  not ;  yet  almost  all  produced 
capsules. 

Linum  usitatissimum  (Linaceae). — Appears  to  be  quite  fertile. 
H.  Hoffmann, '  Bot.  Zeitung,'  1876,  p.  566. 

Trnpatiens  barbiyerum  (Balsaminaceae). — The  flowers,  though  ex- 


Ciiap.  X.     PLANTS   EEKTILE   WITHOUT   INSECT-AID.       367 

cellently  adapted  for  cross-fertilisation  by  tbe  bees  which 
freely  visit  them,  set  abundantly  under  a  net. 

1.  noli-me-tungere  (Balsaminaceas). —  This  species  produces  cleis- 
togene  and  perfect  flowers.  A  plant  was  covered  with  a  net, 
and  some  perfect  flowers,  marked  with  threads,  produced 
eleven  spontaneously  self- fertilised  capsules,  which  contained 
on  an  average  3*45  seeds.  I  neglected  to  ascertain  the 
number  of  seeds  produced  by  perfect  flowers  exposed  to  the 
visits  of  insects,  but  I  believe  it  is  not  greatly  in  excess  ot 
the  above  average.  Mr.  A.  W.  Bennett  has  carefully  described 
the  structure  of  the  flowers  of  I.fulva  in  '  Journal  Linn.  Soc.' 
vol.  xiii.  Bot.  1872,  p.  147.  This  latter  species  is  said  to 
be  sterile  with  its  own  pollen  (f  Gard.  Chronicle,'  1868,  p. 
1286),  and  if  so,  it  presents  a  remarkable  contrast  with  I. 
barbigerum  and  noli-me-tangere. 

Limnanthes  douglasii  (Geraniacese). — Highly  fertile. 

Viscaria  oculuta  (Caryophyllaceas).— Produces  plenty  of  capsules 
with  good  seeds. 

Stellaria  media  (Caryophyllaceas). — Covered-up  and  uncovered 
plants  produced  an  equal  number  of  capsules,  and  the  seeds 
in  both  appeared  equally  numerous  and  good. 

Beta  vulgaris  (Chenopodiaceae). — Highly  self-fertile. 

Vicia  sativa  (Leguminosse). — Protected  and  unprotected  plants 
produced  an  equal  number  of  pods  and  equally  fine  seeds. 
If  there  was  any  difference  between  the  two  lots,  the  covered- 
up  plants  were  the  most  productive. 

V.  hirsuta.  —  This  species  bears  the  smallest  flowers  of  any 
British  leguminous  plant.  The  result  of  covering  up  plants 
was  exactly  the  same  as  in  the  last  species. 

Pisum  sativum  (Leguminosse). — Fully  fertile. 

Lathyrus  odoratus  (Leguminosse). — Fully  fertile. 

L.  nissolia. — Fully  fertile. 

Lupinus  luteus  (Leguminosse). — Fairly  productive. 

h-  pilosus. — Produced  plenty  of  pods. 

Ononis  minutissima  (Leguminosss). — Twelve  perfect  flowers  on  a 
plant  under  a  net  were  marked  by  threads,  and  produced 
eight  pods,  containing  on  an  average  2  "38  seeds.  Pods 
produced  by  flowers  visited  by  insects  would  probably  have 
contained  on  an  average  3 '66  seeds,  judging  from  the  effects 
of  artificial  cross-fertilisation. 

Phaseolus  vulgaris  (Leguminosse). — Quite  fertile. 

Trifolium  arvense  (Leguminosse).— The  excessively  small  flowers 


368       PLANTS   FEETILE   WITHOUT  INSECT- AID.      Chap.  X 

are  incessantly  visited  by  hire  and  humble-bees.  When 
insects  were  excluded  the  flower-heads  seemed  to  produce  as 
many  and  as  fine  seeds  as  the  exposed  heads. 

T.  procumbens. — On  one  occasion  covered-up  plants  seemed  to 
yield  as  many  seeds  as  the  uncovered.  On  a  second  occasion 
sixty  uncovered  flower-heads  yielded  9 "  1  grains  weight  of 
seeds,  whilst  sixty  heads  on  protected  plants  yielded  no  less 
than  17 '7  grains;  so  that  these  latter  plants  were  mnch 
more  productive ;  but  this  result  I  suppose  was  accidental. 
I  have  often  watched  this  plant,  and  have  never  seen  the 
flowers  visited  by  insects ;  but  I  suspect  that  the  flowers  of 
this  species,  and  more  especially  of  Trifolium  minus,  are 
frequented  by  small  nocturnal  moths  which,  as  1  hear  from 
Mr.  Bond,  haunt  the  smaller  clovers. 

Medicago  lupulina  (Leguminoste). — On  account  of  the  danger  of 
losing  the  seeds,  I  was  forced  to  gather  the  pods  before  they 
were  quite  ripe ;  150  flower-lieads  on  plants  visited  by  bees 
yielded  pods  weighing  101  grains;  whilst  150  heads  on 
protected  plants  yielded  pods  weighing  77  grains.  The 
inequality  would  probably  have  been  greater  if  the  mature 
seeds  could  have  been  all  safely  collected  and  compared. 
Ig.  Urban  (Keimung,  Bluthen,  &c,  bei  Medicago,  1873)  has 
described  the  means  of  fertilisation  in  this  genus,  as  has  the 
Bev.  G-.  Henslow  in  the  '  Journal  of  Linn.  Soc.  Bot.'  vol.  ix. 
1866,  pp.  327  and  355. 

Nicotiana  tabacum  (Solanacess). — Fully  self-fertile. 

fpomcea  purpurea  (Convolvulacese). — Highly  self-fertile. 

Leptosiphon  androsaceus  (Polemoniacese). — Plants  under  a  net 
produced  a  good  many  capsules. 

Primula  mollis  (Prirnulacese). — A  non-dim orphic  species,  self-fer- 
tile: J.  Scott,  in 'Journal  Linn.  Soc.  Bot.'  vol.  viii.  1864,  p.  120. 

Nolana  prostrata  (Noknaceas). — Plants  covered  up  in  the  green- 
house, yielded  seeds  by  weight  compared  with  uncovered 
plants,  the  flowers  of  which  were  visited  by  many  bees, 
in  the  ratio  of  100  to  61. 

Ajuga  reptans  (Labiatse). — Set  a  good  many  seeds ;  but  none  of 
the  stems  under  a  net  produced  so  many  as  several  un- 
covered &  terns  growiDg  closely  by. 

Euphrasia  officinalis  (Scrophulariaceae). — Covered-up  plants  pro- 
duced plenty  of  seed ;  whether  less  than  the  exposed  plants  I 
cannot  say.  I  saw  two  small  Dipterous  insects  (Dolic/wpos 
nigripennis  and  Empis  chioptera)  repeatedly  sucking  the 


Chap.  X.      PLANTS   FERTILE    WITHOUT   INSECT-AID.       369 

flowers ;  as  they  crawled  into  them,  they  rubbed  against  the 
bristles  which  project  from  the  anthers,  and  became  dusted 
with  pollen. 

Veronica  ayrestis  (Scrophulariacea3). — Covered-up plants  produced 
an  abundance  of  seeds.  I  do  not  know  whether  any  insects 
visit  the  flowers;  but  I  have  observed  Sjrphidze  repeatedly 
covered  with  pollen  visiting  the  flowers  of  V.  hedercefolia  and 
chamcrdrys. 

Mimulus  luteus  (Scrophulariaceffi). — Highly  self-fertile. 

Calceolaria  (greenhouse  variety)  (Scrophulariacese). — Highly  self- 
fertile. 

Verbascum  thapsus  (Scrophulariacese). — Highly  self-fertile 

V.  lychnitis. — Highly  self-fertile. 

Vandellia  nummular  if olia  (Scrophulariaceas). — Perfect  flowers 
produce  a  good  many  capsules. 

Bartsia  odontites  (Scrophulariacese). — Covered-up  plants  produced 
a  good  many  seeds ;  but  several  of  these  were  shrivelled,  nor 
were  they  so  numerous  as  those  produced  by  unprotected 
plants,  which  were  incessantly  visited  by  hive  and  humble- 
bees. 

Specularia  speculum  (Lobeliacese).  —  Covered  plants  produced 
almost  as  many  capsules  as  the  uncovered. 

Lactucct,  sativa  (Compositse). — Covered  plants  produced  some 
seeds,  but  the  summer  was  wet  and  unfavourable. 

Galium  aparine  (Kubiacese). — Covered  plants  produced  quite  as 
many  seeds  as  the  uncovered. 

Apium  pttroselinum  (Umbelliferae). — Covered  plants  apparently 
were  as  productive  as  the  uncovered. 

Zea  mays  (Graminese). — A  single  plant  in  the  greenhouse 
produced  a  good  many  grains. 

Canna  tvarscewicsi  (Marautacese). — Highly  self-fertile. 

Orchidacece.  —  In  Europe  Ophrys  apifera  is  as  regularly  self- 
fertilised  as  is  any  clcistogene  flower.  In  the  United  States, 
South  Africa,  and  Australia  there  are  a  few  species  which 
are  perfectly  self-fertile.  These  several  cases  are  given  in 
the  2nd  edit,  of  my  work  on  the  Fertilisation  of  Orchids. 

Allium  cepa  (blood  red  var.)  (Liliacese). — Four  flower-heads  were 
covered  with  a  net,  and  they  produced  somewhat  fewer  and 
smaller  capsules  than  those  on  the  uncovered  heads.  The 
capsules  were  counted  on  one  uncovered  head,  and  were  289 
in  number ;  whilst  those  on  a  fine  head  from  under  the  net 
were  only  199. 


370  MEANS  OF   CROSS-FERTILISATION.         Chap.  X. 

Each,  of  these  lists  contains  by  a  mere  accident  the 
same  number  of  genera,  viz.,  forty-nine.  The  genera 
in  the  first  list  include  sixty-five  species,  and  those  in 
the  second  sixty  species ;  the  Orchideae  in  both  being 
excluded.  If  the  genera  in  this  latter  order,  as  well  as 
in  the  Asclepiadse  and  Apocynaceae,  had  been  included, 
the  number  of  species  which  are  sterile  if  insects  are 
excluded  would  have  been  greatly  increased ;  but  the 
lists  are  confined  to  species  which  were  actually  expe- 
rimented on.  The  results  can  be  considered  as  only 
approximately  accurate,  for  fertility  is  so  variable  a 
character,  that  each  species  ought  to  have  been  tried 
many  times.  The  above  number  of  species,  namely, 
125,  is  as  nothing  to  the  host  of  living  plants ;  but 
the  mere  fact  of  more  than  half  of  them  being  sterile 
within  the  specified  degree,  when  insects  are  excluded, 
is  a  striking  one ;  for  whenever  pollen  has  to  be  carried 
from  the  anthers  to  the  stigma  in  order  to  ensure  full 
fertility,  there  is  at  least  a  good  chance  of  cross-fertili- 
sation. I  do  not,  however,  believe  that  if  all  known 
plants  were  tried  in  the  same  manner,  half  would  be 
found  to  be  sterile  within  the  specified  limits;  for 
many  flowers  were  selected  for  experiment  which  pre- 
sented some  remarkable  structure;  and  such  flowers 
often  require  insect-aid.  Thus  out  of  the  forty-nine 
genera  in  the  first  list,  about  thirty-two  have  flowers 
which  are  asymmetrical  or  present  some  remarkable 
peculiarity ;  whilst  in  the  second  list,  including  species 
which  are  fully  or  moderate  y  fertile  when  insects  were 
excluded,  only  about  twenty -one  out  of  the  forty-nine 
are  asymmetrical  or  present   ny  remarkable  peculiarity. 

Means  of  cross-fertilisation. — The  most  important  of 
all  the  means  by  which  jollen  is  carried  from  the 
anthers  to  the  stigma  of  the  same  flower,  or  from  flower 


Chap.  X. 


MEANS   OF   CROSS-FERTILISATION. 


371 


to  flower,  are  insects,  belonging  to  the  orders  of 
Hymenoptera,  Lepidoptera,  and  Diptera ;  and  in  some 
parts  of  the  world,  birds.*  Next  in  importance,  but 
in  a  quite  subordinate  degree,  is  the  wind ;  and  with 
some  aquatic  plants,  according  to  Delpino,  currents  of 
water.  The  simple  fact  of  the  necessity  in  many  cases 
of  extraneous  aid  for  the  transport  of  the  pollen,  and  the 
many  contrivances  for  this  purpose,  render  it  highly 
probable  that  some  great  benefit  is  thus  gained ;  and 
this  conclusion  has  now  been  firmly  established  by  the 
proved  superiority  in  growth,  vigour,  and  fertility  of 
plants  of  crossed  parentage  over  those  of  self-fertilised 
parentage.  But  we  should  always  keep  in  mind  that 
two  somewhat  opposed  ends  have  to  be  gained ;  the 
first  and  more  important  one   being  the   production 


*  I  will  here  give  all  the  cases 
known  to  me  of  Dirds  fertilising 
flowers.  In  South  Brazil,  hum- 
ming-birds certainly  fertilise  the 
various  species  of  Abutilon,  which 
are  sterile  without  their  aid:  (Fritz 
Miiller,  '  Jenaische  Zeitschrift  f. 
Naturwiss.'  B.  vii.  1872,  p.  24.) 
Long-beaked  humming-birds  visit 
the  flowers  of  Brugmansia,  whilst 
some  of  the  short-beaked  species 
often  penetrate  its  large  corolla  in 
order  to  obtain  the  nectar  in  an 
illegitimate  manner,  in  the  same 
manner  as  do  bees  in  all  parts  of 
the  world.  It  appears,  indeed, 
thdt  the  beaks  of  humming-birds 
are  specially  adapted  to  the  va- 
rious kinds  of  flowers  which  they 
visit :  on  the  Cordillera  they  suck 
the  Salvia?,  and  lacerate  the 
flowers  of  the  Tacsonise ;  in  Nica- 
ragua, Mr.  Belt  saw  them  sucking 
the  flowers  of  Marcgravia  and 
Erythrina,  and  thus  they  carried 
pollen  from  flower  to  flower.  In 
North  America  they  are  said  to 
frequent  the  flowers  of  Impatiens : 
(Gould,  '  Introduction  to  the  Tro- 


choids,' 1861,  pp.  15, 120 ;  '  Gard. 
Chronicle,'  1869,  p.  389;  'The 
Naturalist  in  Nicaragua,'  p.  129 ; 
'  Journal  of  Linn.  Soc.  Bot.'  vol. 
xiii.  1872,  p.  151.)  I  may  add 
that  I  often  saw  in  Chile  a  Mimus 
with  its  head  yellow  with  pollen 
from,  as  I  believe,  a  Cassia.  I 
have  been  assured  that  at  the 
Cape  of  Good  Hope,  Strelitzia  is 
fertilised  by  the  Nectarinidse. 
There  can  hardly  be  a  doubt  that 
many  Australian  flowers  are  fer- 
tilised by  the  many  honey-sucking 
birds  of  that  country.  Mr.  Wal- 
lace remarks  (address  to  the  Bio- 
logical Section,  Brit.  Assoc.  1876) 
that  he  has  "often  observed  the 
beaks  and  faces  of  the  brush- 
tongued  lories  of  the  Moluccas 
covered  with  pollen."  In  New 
Zealand,  many  specimens  of  the 
Antliornis  melanura  had  their 
heads  coloured  with  pollen  from 
the  flowers  of  an  endemic  species 
of  Fuchsia  :  (Potts,  '  Transact. 
New  Zealand  Institute,'  vol.  iii. 
1870,  p.  72.) 


372  MEANS   OF   CKOSS-FEKTILISATTON.  Chap.  X. 

of  seeds  by  any  means,  and  the  second,  cross- ferti- 
lisation. 

The  advantages  derived  from  cross-fertilisation  throw 
a  flood  of  light  on  most  of  the  chief  characters  of  flowers. 
We  can  thus  understand  their  large  size  and  bright 
colours,  and  in  some  cases  the  bright  tints  of  the  ad- 
joining parts,  such  as  the  peduncles,  bractese,  &c.  By 
this  means  they  are  rendered  conspicuous  to  insects, 
on  the  same  principle  that  almost  every  fruit  which  is 
devoured  by  birds  presents  a  strong  contrast  in  colour 
with  the  green  foliage,  in  order  that  it  may  be  seen, 
and  its  seeds  freely  disseminated.  With  some  flowers 
conspicuousness  is  gained  at  the  expense  even  of  the 
reproductive  organs,  as  with  the  ray-florets  of  many 
Composite,  the  exterior  flowers  of  Hydrangea,  and  the 
terminal  flowers  of  the  Feather-hyacinth  or  Muscari. 
There  is  also  reason  to  believe,  and  this  was  the  opinion 
of  Sprengel,  that  flowers  differ  in  colour  in  accordance 
with  the  kinds  of  insects  which  frequent  them. 

Not  only  do  the  bright  colours  of  flowers  serve  to 
attract  insects,  but  dark-coloured  streaks  and  marks 
are  often  present,  which  Sprengel  long  ago  maintained 
served  as  guides  to  the  nectary.  These  marks  follow 
the  veins  in  the  petals,  or  lie  between  them.  They 
may  occur  on  only  one,  or  on  all  excepting  one  or 
more  of  the  upper  or  lower  petals ;  or  they  may  form 
a  dark  ring  round  the  tubular  part  of  the  corolla,  or 
be  confined  to  the  lips  of  an  irregular  flower.  In  the 
white  varieties  of  many  flowers,  such  as  of  Digitalis 
purpurea,  Antirrhinum  majus,  several  species  of  Dian- 
thus,  Phlox,  Myosotis,  Rhododendron,  Pelargonium, 
Primula  and  Petunia,  the  marks  generally  persist, 
whilst  the  rest  of  the  corolla  has  become  of  a  pure 
white  ;  but  this  may  be  due  merely  to  their  colour 
being  more  intense  and  thus  less  readily  obliterated. 


Chap.  X.         MEANS   OF   CROSS-FERTILISATION.  373 

Sprengel's  notion  of  the  use  of  these  marks  as  guides 
appeared  to  me  for  a  long  time  fanciful ;  for  insects, 
without  such  aid,  readily  discover  and  bite  holes 
through  the  nectary  from  the  outside.  They  also 
discover  the  minute  nectar-secreting  glands  on  the 
stipules  and  leaves  of  certain  plants.  Moreover,  some 
few  plants,  such  as  certain  poppies,  which  are  not 
nectariferous,  have  guiding  marks;  but  we  might 
perhaps  expect  that  some  few  plants  would  retain 
traces  of  a  former  nectariferous  condition.  On  the  other 
hand,  these  marks  are  much  more  common  on  asymme- 
trical flowers,  the  entrance  into  which  would  be  apt  to 
puzzle  insects,  than  on  regular  flowers.  Sir  J.  Lubbock 
has  also  proved  that  bees  readily  distinguish  colours, 
and  that  they  lose  much  time  if  the  position  of  honey 
which  they  have  once  visited  be  in  the  least  changed.* 
The  following  case  affords,  I  think,  the  best  evidence 
that  these  marks  have  really  been  developed  in  corre- 
lation with  the  nectary.  The  two  upper  petals  of  the 
common  Pelargonium  are  thus  marked  near  their  bases; 
and  I  have  repeatedly  observed  that  when  the  flowers 
vary  so  as  to  become  peloric  or  regular,  they  lose  their 
nectaries  and  at  the  same  time  the  dark  marks. 
When  the  nectary  is  only  partially  aborted,  only  one 
of  the  upper  petals  loses  its  mark.  Therefore  the  nec- 
tary and  these  marks  clearly  stand  in  some  sort  of  close 
relation  to  one  another  ;  and  the  simplest  view  is  that 
they  were  developed  together  for  a  special  purpose; 
the  only  conceivable  one  being  that  the  marks  serve  as 
a  guide  to  the  nectary.  It  is,  however,  evident  from 
what  has  been  already  said,  that  insects  could  discover 
the  nectar  without  the  aid  of  guiding  marks.  They 
are  of  service  to  the  plant,  only  by  aiding  insects  to 

*  '  British  Wild  Flowers  in  relation  to  Insects,'  1875,  p.  44. 


374  MEANS   OF   CEOSS-FEETILISATION.  Chap.  X. 

visit  and  suck  a  greater  number  of  flowers  within  a 
given  time  than  would  otherwise  be  possible ;  and  thus 
there  will  be  a  better  chance  of  fertilisation  by  pollen 
brought  from  a  distinct  plant,  and  this  we  know  is  of 
paramount  importance. 

The  odours  emitted  by  flowers  attract  insects,  as  I 
have  observed  in  the  case  of  plants  covered  by  a  muslin 
net.  Nageli  affixed  artificial  flowers  to  branches, 
scenting  some  with  essential  oils  and  leaving  others 
unscented ;  and  insects  were  attracted  to  the  former  in 
an  unmistakable  manner.*  Not  a  few  flowers  are  both 
conspicuous  and  odoriferous.  Of  all  colours,  white  is 
the  prevailing  one;  and  of  white  flowers  a  considerably 
larger  proportion  smell  sweetly  than  of  any  other 
colour,  namely,  14  ■  6  per  cent. ;  of  red,  only  8  ■  2  per 
cent,  are  odoriferous.f  The  fact  of  a  larger  proportion 
of  white  flowers  smelling  sweetly  may  depend  in  part 
on  those  which  are  fertilised  by  moths  requiring  the 
double  aid  of  conspicuousness  in  the  dusk  and  of 
odour.  So  great  is  the  economy  of  nature,  that  most 
flowers  which  are  fertilised  by  crepuscular  or  nocturnal 
insects  emit  their  odour  chiefly  or  exclusively  in  the 
evening.  Some  flowers,  however,  which  are  highly 
odoriferous  depend  solely  on  this  quality  for  their  fer- 
tilisation, such  as  the  night-flowering  stock  (Hesperis) 
and  some  species  of  Daphne  ;  and  these  present  the 
rare  case  of  flowers  which  are  fertilised  by  insects  being 
obscurely  coloured. 

The  storage  of  a  supply  of  nectar  in  a  protected  place 
is  manifestly  connected  with  the  visits  of  insects.  So 
is  the  position  which  the  stamens  and  pistils  occupy, 

*  '  Enstehung,  &c,  der  Natur-  and    by   Schubler    and    Kohler. 

hist.  Art.'    1865,  p.  23.  I   have  not  seen    their   original 

t  The  colours   and  odours   of  •works,  but   a  very  full  abstract 

the  flowers  of  4200  species  have  is  given  in  Loudun's  '  Gardener's 

been    tabulated    by   Laudgrabe,  Mag.'  vol.  xiii.  1837,  p.  367. 


Chap.  X.         MEANS   OF   CKOSS-FEKTILISATION.  375 

either  permanently  or  at  the  proper  period  through 
their  own  movements  ;  for  when  mature  they  invariably 
stand  in  the  pathway  leading  to  the  nectary.  The 
shape  of  the  nectary  and  of  the  adjoining  parts  are 
likewise  related  to  the  particular  kinds  of  insects  which 
habitually  visit  the  flowers ;  this  has  been  well  shown 
by  H.  Miiller  by  his  comparison  of  lowland  species 
which  are  chiefly  visited  by  bees,  with  alpine  species 
belonging  to  the  same  genera  which  are  visited  by 
butterflies.*  Flowers  may  also  be  adapted  to  certain 
kinds  of  insects,  by  secreting  nectar  particularly  attrac- 
tive to  them,  and  unattractive  to  other  kinds ;  of  which 
fact  Epipactis  latifolia  offers  the  most  striking  instance 
known  to  me,  as  it  is  visited  exclusively  by  wasps. 
Structures  also  exist,  such  as  the  hairs  within  the 
corolla  of  the  foxglove  (Digitalis),  which  apparently 
serve  to  exclude  insects  that  are  not  well  fitted  to  bring 
pollen  from  one  flower  to  another.!  I  need  say  nothing 
here  of  the  endless  contrivances,  such  as  the  viscid 
glands  attached  to  the  pollen-masses  of  the  Orchidese 
and  Asclepiadse,  or  the  viscid  or  roughened  state  of 
the  pollen-grains  of  many  plants,  or  the  irritability  of 
their  stamens  which  move  when  touched  by  insects,  &c, 
— as  all  these  contrivances  evidently  favour  or  ensure 
cross-fertilisation. 

All  ordinary  flowers  are  so  far  open  that  insects  can 
force  an  entrance  into  them,  notwithstanding  that 
some,  like  the  Snapdragon  (Antirrhinum),  various 
Papilionaceous  and  Fumariaceous  flowers,  are  in 
appearance  closed.  It  cannot  be  maintained  that  their 
openness  is  necessary  for  fertility,  as  cleistogene  flowers 
which  are  permanently  closed  yield  a  full  complement 
of  seeds.     Pollen  contains  much  nitrogen  and   phos- 

*  'Nature,'  1874,  p.  110;  1875,  f  Belt,  'The  Naturalist  in  Ni- 

p.  19.J;  1S7G,  pp.  210,  289.  caragua,'  1874,  p.  132. 

17 


376  MEANS   OF   CROSS-FERTILISATION.  Chap.  X 

phorus — the  two  most  precious  of  all  the  elements  for 
the  growth  of  plants — but  in  the  case  of  most  open 
flowers,  a  large  quantity  of  pollen  is  consumed  by 
pollen-devouring  insects,,  and  a  large  quantity  is 
destroyed  during  long-continued  rain.  With  many 
plants  this  latter  evil  is  guarded  against,  as  far  as 
is  possible,  by  the  anthers  opening  only  during  dry 
weather,* — by  the  position  and  form  of  some  or  all  of 
the  petals, — by  the  presence  of  hairs,  &c,  and  as  Kerner 
has  shown  in  his  interesting  essay,t  by  the  movements 
of  the  petals  or  of  the  whole  flower  during  cold  and  wet 
weather.  In  order  to  compensate  the  loss  of  pollen  in 
so  many  ways,  the  anthers  produce  a  far  larger  amount 
than  is  necessary  for  the  fertilisation  of  the  same  flower. 
I  know  this  from  my  own  experiments  on  Ipomoea, 
given  in  the  Introduction  ;  aud  it  is  still  more  plainly 
shown  by  the  astonishingly  small  quantity  produced . 
by  cleistogene  flowers,  which  lose  none  of  their  pollen, 
in  comparison  with  that  produced  by  the  open  flowers 
borne  by  the  same  plants  ;  and  yet  this  small  quantity 
suffices  for  the  fertilisation  of  all  their  numerous  seeds. 
Mr.  Hassall  took  pains  in  estimating  the  number  of 
pollen-grains  produced  by  a  flower  of  the  Dandelion 
(Leontodon),  and  found  the  number  to  be  243,600, 
and  in  a  Paeony  3,654,000  grains.!  The  editor 
of  the  '  Botanical  Register '  counted  the  ovules  in  the 
flowers  of    Wistaria  sinensis,  and  carefully  estimated 


*_Mr.  BlacMey  observed  that  up  in  the  atmosphere,  during  the 
the  ripe  anthers  of  rye  did  not  first  fine  and  dry  days  after  wet 
dehisce  whilst  kept  under  a  bell-  weather,  than  at  other  times  : 
glass  in  a  damp  atmosphere,  '  Experimental  Researches  on 
whilst  other  antheis  exposed  to  Hay  Fever,'  1873,  p.  127. 
the  same  temperature  in  the  open  t  'Die  Schutzmittel  des  Pol- 
air  dehisced  freely.    Healsofound  lens,' 1873. 

much   more   pollen   adhering  to  %  'Annals  and   Mag.   of  Nat. 

the    sticky    slLles,   which    were  Hist.'  vol.  viii.  1842,  p.  108. 
attached  to  kites  and  sent  hiirh 


Chap.  X.         MEANS   OF    CEOSS-FEE  TILISATION.  377 

the  number  of  pollen- grains,  and  he  found  that  for  each 
ovule  there  were  7,000  grains.*  With  Mirabilis,  three 
or  four  of  the  very  large  pollen-grains  are  sufficient  to 
fertilise  an  ovule ;  but  I  do  not  know  how  many  grains 
a  flower  produces.  With  Hibiscus,  Kolreuter  found 
that  sixty  grains  were  necessary  to  fertilise  all  the  ovules 
of  a  flower,  and  he  calculated  that  4863  grains  were 
produced  by  a  single  flower,  or  eighty-one  times  too 
many.  With  Geum  urbanum,  however,  according  to 
Gartner,  the  pollen  is  only  ten  times  too  much.f  As 
we  thus  see  that  the  open  state  of  all  ordinary  flowers, 
and  the  consequent  loss  of  much  pollen,  necessitate  the 
development  of  so  prodigious  an  excess  of  this  precious 
substance,  why,  it  may  be  asked,  are  flowers  always  left- 
open  ?  As  many  plants  exist  throughout  the  vegetable 
kingdom  which  bear  cleistogene  flowers,  there  can 
hardly  be  a  doubt  that  all  open  flowers  might  easily 
have  been  converted  into  closed  ones.  The  graduated 
steps  by  which  this  process  could  have  been  effected 
may  be  seen  at  the  present  time  in  Lathyrus  nissolia, 
Biophytum  sensitivum,  and  several  other  plants.  The 
answer  to  the  above  question  obviously  is,  that  with 
permanently  closed  flowers  there  could  be  no  cross- 
fertilisation. 

The  frequency,  almost  regularity,  with  which  pollen 
is  transported  by  insects  from  flower  to  flower,  often 
from  a  considerable  distance,  well  deserves  attention.! 


*  Quoted    in   '  Gard.    Chron.'  mature.     Kolreuter  marked  310 

1846,  p.  771.  flowers,     and    put    pollen    from 

+  Kolreuter, '  Vorlaufige  Nach-  other    flowers    on   their  stigmas 

richt,'  1761,  p.  9.    Gartner, '  Beit-  every    day,   so    that    they    were 

rage  zur  Kenntniss,'  &c.  p.  346.  thoroughly  fertilised;  and  he  left 

%  An  experiment  made  by  Kill-  the  same  number  of  other  flowers 

reuter   (' Fortsetsung,'  &c.    1763,  to  the  agency  of  insects.    After- 

p.   69)  affords  good  evidence  on  wards  he  counted  the   seeds   of 

this  head.     Hibiscus  vesicarius  is  both  lots :  the  flowers  which  he 

strongly  dichogamous,  its  pollen  had  fertilised  with  such  astorusli- 

being  shed  before  the  stigmas  are  ing  care  produced   '  1,237  seeds. 


'678  MEANS   OF   CKOSS-FERTTLISATION.  Chap.  X. 

This  is  best  shown  by  the  impossibility  in  many  cases 
of  raising  two  varieties  of  the  same  species  pure,  if  they 
grow  at  all  near  together ;  but  to  this  subject  I  shall 
presently  return ;  also  by  the  many  cases  of  hybrids 
which  have  appeared  spontaneously  both  in  gardens  and 
a  state  of  nature.  With  respect  to  the  distance  from 
which  pollen  is  often  brought,  no  one  who  has  had  any 
experience  would  expect  to  obtain  pure  cabbage-seed, 
for  instance,  if  a  plant  of  another  variety  grew  within 
two  or  three  hundred  yards.  An  accurate  observer, 
the  late  Mr.  Masters  of  Canterbury,  assured  me  that 
he  once  had  his  whole  stock  of  seeds  "  seriously  affected 
with  purple  bastards,"  by  some  plants  of  purple  kale 
which  flowered  in  a  cottager's  garden  at  the  distance  of 
half  a  mile ;  no  other  plant  of  this  variety  growing  any 
nearer.*  But  the  most  striking  case  which  has  been  re- 
corded is  that  by  M.  Godron,|  who  shows  by  the  nature 
of  the  hybrids  produced  that  Primula  grandijiora  must 
have  been  crossed  with  pollen  brought  by  bees  from 
P.  officinalis,  growing  at  the  distance  of  above  two 
kilometres,  or  of  about  one  English  mile  and  a  quarter. 
All  those  who  have  long  attended  to  hybridisation, 
insist  in  the  strongest  terms  on  the  liability  of  castrated 
flowers  to  be  fertilised  by  pollen  brought  from  distant 
plants  of  the  same  species.^    The  following  case  shows 

whilst  those  left  to  the  insects  the  proper  posit:on  for  fertilising 

produced  10,S8(J  ;   that  is,  a  less  the  flowers  of  this  species,  on  an 

number  by   only  351 ;    ami   this  island   in   Derwentwater,  at   the 

small  inferiority  is  fully  accounted  distance  of  half  a  mile  from  any 

for    l>y   the    insects   not    having  place    where    this    plant    grew  : 

7<>ike  1  during  some   days,  when  'Nature,'  1872,  p.  393. 
t  e  weather  was  cold  with  con-  t  'Revue  des  Sc.  Nat.'    1875, 

tinued  rain.  p.  331. 

*  Mr.  W.  C.  Marshall  caught  J  See,  for  instance,  the  remarks 

no  less  than  seven  specimens  of  a  by     Herbert,     '  Amaryllidacese,' 

moth  (Cucullia  unibraflca)  with  1837,    p.    349.      Also    Gartner's 

the  pollinia  of  the  bntterfly-oro!  is  sirong  expressions  on  this  subject 

(Hubenana   ehloiantha)   sticking  in  hin  '  Bastarderzeugung,'  184.9, 

to   their  eyes,  and,  therefore,  in  p.  67Q ;   and  '  Kenntniss  der  Be- 


Chap.  X.         MEANS   OF   CROSS-FERTILISATION.  379 

this  in  the  clearest  manner :  Gartner,  before  he  had 
gained  much  experience,  castrated  and  fertilised  520 
flowers  on  various  species  with  pollen  of  other  genera 
or  other  species,  but  left  them  unprotected  ;  for,  as  he 
says,  he  thought  it  a  laughable  idea  that  pollen  should 
be  brought  from  flowers  of  the  same  species,  none  of 
which  grew  nearer  than  between  500  and  600  yards.* 
The  result  was  that  289  of  these  520  flowers  yielded  no 
seed,  or  none  that  germinated  ;  the  seed  of  29  flowers 
produced  hybrids,  such  as  might  have  been  expected 
from  the  nature  of  the  pollen  employed ;  and  lastly, 
the  seed  of  the  remaining  202  flowers  produced  per- 
fectly pure  plants,  so  that  these  flowers  must  have 
been  fertilised  by  pollen  brought  by  insects  from  a 
distance  of  between  500  and  600  yards.t  It  is  of 
course  possible  that  some  of  these  202  flowers  might 
have  been  fertilised  by  pollen  left  accidentally  in 
them  when  they  were  castrated ;  but  to  show  how 
improbable  this  is,  I  may  add  that  Gartner,  during  the 
next  eighteen  years,  castrated  no  less  than  8042  flowers 
and  hybridised  them  in  a  closed  room ;  and  the  seeds 
from  only  seventy  of  these,  that  is  considerably  less 
than  1  per  cent.,  produced  pure  or  unhybridised 
offspring.! 


fruchtung,'  1844,  pp.  510,  573.  t  Henschel's  experiments 
Also  Lecoq,  '  De  la  Fecondation,'  (quoted  by  Gartner,  '  Kenntniss,' 
&c,  1845,  p.  27.  Some  statements  &c,  p.  574),  which  are  worthless 
have  been  published  during  late  in  all  other  respects,  likewise 
years  of  the  extraordinary  ten-  show  bow  largely  flowers  are  in- 
dency  of  hybrid  plants  to  revert  tercrossed  by  insects.  He  cas- 
to  their  parent  forms;  but  as  it  is  trated  many  flowers  on  thirty- 
not  said  how  the  fluwers  were  seven  species,  belonging  to  twenty- 
protected  from  insects,  it  may  be  two  genera,  and  put  on  their 
suspected  that  they  were  often  stigmas  either  no  pollen,  or  pollen 
feitilised  with  pollen  brought  from  distinct  genera,  yet  they  all 
from  a  distance  Irom  the  parent-  seeded,  and  all  the  seedlings  raised 
species.  from  them  were  of  course  pure. 

*  '  Kenntniss  der  Befruchtung,'  J  '  Kenntniss,'  &c.  pp.  555,  576, 
pp.  539,  550,  575,  576. 


380  MEANS   OF   CROSS-FEETTLISATTON.         Chap.  X. 

From  the  various  facts  now  given,  it  is  evident  that 
most  flowers  are  adapted  in  an  admirable  manner  for 
cross-fertilisation.  Nevertheless,  the  greater  number 
likewise  present  structures  which  are  manifestly- 
adapted,  though  not  in  so  striking  a  manner,  for  self- 
fertilisation.  The  chief  of  these  is  their  hermaphrodite 
condition ;  that  is,  their  including  within  the  same 
corolla  both  the  male  and  female  reproductive  organs. 
These  often  stand  close  together  and  are  mature  at 
the  same  time ;  so  that  pollen  from  the  same  flower 
cannot  fail  to  be  deposited  at  the  proper  period  on  the 
stigma.  There  are  also  various  details  of  structure 
adapted  for  self-fertilisation.*  Such  structures  are 
best  shown  in  those  curious  cases  discovered  by  H. 
Miiller,  in  which  a  species  exists  under  two  forms, — 
one  bearing  conspicuous  flowers  fitted  for  cross-fertilisa- 
tion, and  the  other  smaller  flowers  fitted  for  self-fer- 
tilisation, with  many  parts  in  the  latter  slightly 
modified  for  this  special  purpose.t 

As  two  objects  in  most  respects  opposed,  namely, 
cross-fertilisation  and  self-fertilisation,  have  in  many 
cases  to  be  gained,  we  can  understand  the  co-existence 
in  so  many  flowers  of  structures  which  appear  at  first 
sight  unnecessarily  complex  and  of  an  opposed  nature. 
We  can  thus  understand  the  great  contrast  in  structure 
between  cleistogene  flowers,  which  are  adapted  exclu- 
sively for  self-fertilisation,  and  ordinary  flowers  on  the 
same  plant,  which  are  adapted  so  as  to  allow  of  at  least 
occasional  cross-fertilisation.:]:     The  former  are  always 


*  H.  Miiller, 'Die Befruchtung,'  of  the  plants   which   bear  cleis- 

&e.  p.  448.  togene   and  perfect  flowers.     He 

f  '  Nature,'  1873,  pp.  44,  433.  finds  in  the  nests  of  Termites   in 

j  Fritz  Miiller  has  discovered  Brazil,  males   and  females  with 

in    the    animal    kingdom   ( '  Je-  imperfect   wings,   which    do   not 

naische  Zeitsehr.'  B.  iv.  p.  451)  leave  the  nests  and  propagate  tho 

e.  case  curiously  analogous  to  that  species  in  a  cleistogene  manner 


Our.  X.  CROSS-FERTILISATION.  381 

minute,  completely  closed,  with  their  petals  more  or 
less  rudimentary  and  never  brightly  coloured ;  they 
never  secrete  nectar,  never  are  odoriferous,  have  very 
small  anthers  which  produce  only  a  few  grains  of  pollen, 
and  their  stigmas  are  but  little  developed.  Bearing 
in  mind  that  some  flowers  are  cross-fertilised  by  the 
wind  (called  anemophilous  by  Delpino),  and  others 
by  insects  (called  entomophilous),  we  can  further 
understand,  as  was  pointed  out  by  me  several  years 
ago,*  the  great  contrast  in  appearance  between  these 
two  classes  of  flowers.  Anemophilous  flowers  resemble 
in  many  respects  cleistogene  flowers,  but  differ  widely 
in  not  being  closed,  in  producing  an  extraordinary 
amount  of  pollen  which  is  always  incoherent,  and 
in  the  stigma  often  being  largely  developed  or 
plumose.  We  certainly  owe  the  beauty  and  odour  of 
our  flowers  and  the  storage  of  a  large  supply  of  honey 
to  the  existence  of  insects. 

On  the  Relation  behveen  the  Structure  and  Conspicuous- 
ness  of  Floivers,  the  Visits  of  Insects,  and  the  Advan- 
tages of  Cross-fertilisation. 

It  has  already  been  shown  that  there  is  no  close 
relation  between  the  number  of  seeds  produced  by 
flowers  when  crossed  and  self-fertilised,  and  the  degree 
to  which  their  offspring  are  affected  by  the  two  pro- 
cesses. I  have  also  given  reasons  for  believing  that 
the  inefficiency  of  a  plant's  own  pollen  is  in  most  cases 


but  only  if  a  fully-developed  queen  almost  infinite  numbers  by  a  host 

after    swarming    does  not   enter  of  enemies,  so  th.it  a  queen  may 

the    old    nest.     The    fully-deve-  often  fail  to  enter  an  old  nest; 

loped    males    and    females     are  and   then   the  imperfectly  deve- 

■winged,  and  individuals  from  did-  loped  males  and  females  propagate 

tinct   nests  can  hardly  fail  often  and  keep  up  the  stock. 
to     intercross.     In     the     act     of  *  '  Journal  of  Linn.  Soe.'  vol 

swarming  they  are    destroyed   in  vii.  Bot.  1863,  p.  77. 


382  CEOSS-FERTILISATION.  Chap.  X. 

an  incidental  result,  or  has  not  been  specially  acquired 
for  the  sake  of  preventing  self-fertilisation.  On  the 
other  hand,  there  can  hardly  be  a  doubt  that  dichogamy, 
which  prevails  according  to  Hildebrand*  in  the  greater 
number  of  species, — that  the  heterostyled  condition  of 
certain  plants, — and  that  many  mechanical  structures 
— have  all  been  acquired  so  as  both  to  check  self- 
fertilisation  and  to  favour  cross-fertilisation.  The 
means  for  favouring  cross-fertilisation  must  have  been 
acquired  before  those  which  prevent  self-fertilisation  ; 
as  it  would  manifestly  be  injurious  to  a  plant  that 
its  stigma  should  fail  to  receive  its  own  pollen, 
unless  it  had  already  become  well  adapted  for  receiv- 
ing pollen  from  another  individual.  It  should  be 
observed  that  many  plants  still  possess  a  high  power 
of  self-fertilisation,  although  their  flowers  are  excel- 
lently constructed  for  cross-fertilisation — for  instance, 
those  of  many  papilionaceous  species. 

It  may  be  admitted  as  almost  certain  that  some 
structures,  such  as  a  narrow  elongated  nectary,  or  a 
long  tubular  corolla,  have  been  developed  in  order 
that  certain  kinds  of  insects  alone  should  obtain  the 
nectar.  These  insects  would  thus  find  a  store  of  nectar 
preserved  from  the  attacks  of  other  insects ;  and 
they  would  thus  be  led  to  visit  frequently  such 
flowers  and  to  carry  pollen  from  one  to  the  other,  f 
It  might  perhaps  have  been  expected  that  plants 
having  their  flowers  thus  peculiarly  constructed  would 
profit  in  a  greater  degree  by  being  crossed,  than 
ordinary  or  simple  flowers ;  but  this  does  not  seem 
to  hold  good.  Thus  Tropzeolum  minus  has  a  long 
nectary  and   an   irregular   corolla,  whilst  Limnanthes 


*  '  Die  Geschlechter  Vertheil-       on    this   subject   by    H.   Miiller, 
ung,'  &c.  p.  32  '  Die  Befrucktung,'  &c.  p.  431. 

f  See  the  interesting  discussion 


Chap.  X.  INCONSPICUOUS   FLOWEES.  383 

douglasii  has  a  regular  flower  and  no  proper  nectary, 
yet  the  crossed  seedlings  of  both  species  are  to  the 
self-fertilised  in  height  as  100  to  79.  Salvia  coccinea 
has  an  irregular  corolla,  with  a  curious  apparatus  by 
which  insects  depress  the  stamens,  while  the  flowers 
of  Ipomoea  are  regular ;  and  the  crossed  seedlings  of 
the  former  are  in  height  to  the  self-fertilised  as 
100  to  76,  whilst  those  of  the  Ipomoea  are  as  100  to 
77.  Fagopyrum  is  dimorphic,  and  Anagallis  collina  is 
non-dimorphic,  and  the  crossed  seedlings  of  both  are 
in  height  to  the  self- fertilised  as  100  to  69. 

With  all  European  plants,  excepting  the  compara- 
tively rare  anemophilous  kinds,  the  possibility  of 
distinct  individuals  intercrossing  depends  on  the 
visits  of  insects ;  and  H.  Miiller  has  proved  by  his 
valuable  observations,  that  large  conspicuous  flowers 
are  visited  much  more  frequently  and  by  many  more 
kinds  of  insects,  than  are  small  inconspicuous  flowers. 
He  further  remarks  that  the  flowers  which  are  rarely 
visited  must  be  capable  of  self-fertilisation,  otherwise 
they  would  quickly  become  extinct.  *  There  is,  how- 
ever, some  liability  to  error  in  forming  a  judgment 
on  this  head,  from  the  extreme  difficulty  of  ascertain- 
ing whether  flowers  which  are  rarely  or  never  visited 
during  the  day  (as  in  the  above  given  case  of  Fwnaria 
capreolata)  are  not  visited  by  small  nocturnal  Lepi- 
doptera,  which  are  known  to  be  strongly  attracted  by 
sugar,  t  The  two  lists  given  in  the  early  part  of 
this  chapter  support  Miiller's  conclusion  that  small 
and   inconspicuous  flowers  are  completely  selt-fertile  : 


*  '  Befruchtung,'    &c,    p.  426.  collector  of  Noctuse,   come  very 

'  Nature,' 1873,  p.  433.  freely   to   sug;ir,   mid    no    doubt 

f  In  answer  to  a  question  by  naturally  visit  Mowers:"  the  'En- 

me,  the  editor  of  an  entomological  tomologists'  Weekly  Intelligencer, 

journal   writes  —  "The    Depivs-  1860,  p.  103. 
eariae,   as  is  notorious  to    every 


884  CKOSS-FEKTILISATTON.  Chap.  X. 

for  only  eight  or  nine  out  of  the  125  species  in  the 
two  lists  come  under  this  head,  and  all  of  these  were 
proved  to  be  highly  fertile  when  insects  were  excluded. 
The  singularly  inconspicuous  flowers  of  the  Ely 
Ophrys  (0.  muscifera),  as  I  have  elsewhere  shown,  are 
rarely  visited  by  insects  ;  and  it  is  a  strange  instance  of 
imperfection,  in  contradiction  to  the  above  rule,  that 
these  flowers  are  not  self-fertile,  so  that  a  large  pro- 
portion of  them  do  not  produce  seeds.  The  converse 
of  the  rule  that  plants  bearing  small  and  inconspicuous 
flowers  are  self-fertile,  namely,  that  plants  with  large 
and  conspicuous  flowers  are  self-sterile,  is  far  from  true, 
as  may  be  seen  in  our  second  list  of  spontaneously 
self-fertile  species  ;  for  this  list  includes  such  species  as 
Ipomoea  purpurea,  Adonis  sestivalis,  Verbascum  thapsus, 
Visum  sativum,  Lathyrus  odoratus,  some  species  of 
Papaver  and  of  Nymphsea,  and  others. 

The  rarity  of  the  visits  of  insects  to  small  flowers, 
does  not  depend  altogether  on  their  inconspicuousness, 
but  likewise  on  the  absence  of  some  sufficient  attraction ; 
for  the  flowers  of  Trifolium  arvense  are  extremely 
small,  yet  are  incessantly  visited  by  hive  and  humble- 
bees,  as  are  the  small  and  dingy  flowers  of  the 
asparagus.  The  flowers  of  Linaria  cymbalaria  are 
small  and  not  very  conspicuous,  yet  at  the  proper  time 
they  are  freely  visited  by  hive-bees.  I  may  add  that, 
according  to  Mr.  Bennett,*  there  is  another  and  quite 
distinct  class  of  plants  which  cannot  be  much  frequented 
by  insects,  as  they  flower  either  exclusively  or  often 
during  the  winter,  and  these  seem  adapted  for  self- 
fertilisation,  as  they  shed  their  pollen  before  the  flowers 
expand. 

That  many  flowers  have  been  rendered  conspicuous 


'  Nitture,'  1869,  p.  11. 


Chap.  X.  INCONSPICUOUS  FLOWEKS.  385 

for  the  sake  of  guiding  insects  to  them  is  highly 
probable  or  almost  certain  ;  but  it  may  be  asked,  have 
other  flowers  been  rendered  inconspicuous  so  that  they 
may  not  be  frequently  visited,  or  have  they  merely 
retained  a  former  and  primitive  condition  ?  If  a  plant 
were  much  reduced  in  size,  so  probably  would  be  the 
flowers  through  correlated  growth,  and  this  may  possibly 
account  for  some  cases ;  but  the  size  and  colour  of  the 
corolla  are  both  extremely  variable  characters,  and  it 
can  hardly  be  doubted  that  if  large  and  brightly- 
coloured  flowers  were  advantageous  to  any  species, 
these  could  be  acquired  through  natural  selection 
within  a  moderate  lapse  of  time,  as  indeed  we  see  with 
most  alpine  plants.  Papilionaceous  flowers  are  mani- 
festly constructed  in  relation  to  the  visits  of  insects, 
and  it  seems  improbable,  from  the  usual  character  of 
the  group,  that  the  progenitors  of  the  genera  Yicia 
and  Trifolium  produced  such  minute  and  unattractive 
flowers  as  those  of  V.  lursuta  and  T.  procunibens.  We 
are  thus  led  to  infer  that  some  plants  either  have  not 
had  their  flowers  increased  in  size,  or  have  actually 
had  them  reduced  and  purposely  rendered  incon- 
spicuous, so  that  they  are  now  but  little  visited  by 
insects.  In  either  case  they  must  also  have  acquired 
or  retained  a  high  degree  of  self-fertility. 

If  it  became  from  any  cause  advantageous  to  a  spe- 
cies to  have  its  capacity  for  self-fertilisation  increased, 
there  is  little  difficulty  in  believing  that  this  could 
readily  be  effected;  for  three  cases  of  plants  varying 
in  such  a  manner  as  to  be  more  fertile  with  their  own 
pollen  than  they  originally  were,  occurred  in  the 
course  of  my  few  experiments,  namely,  with  Mimulus, 
lpomoea,  and  Nicotiana.  Nor  is  there  any  reason  to 
doubt  that  many  kinds  of  plants  are  capable  under 
favourable  circumstances   of  propagating   themselves 


386  CROSS-FERTILISATION.  Chap.  X. 

for  very  many  generations  by  self-fertilisation.  This 
is  the  case  with  the  varieties  of  Piaum  sativum  and 
of  Lathy rus  odoratus  which  are  cultivated  in  England, 
and  with  Ophrys  apifera  and  some  other  plants  in  a 
state  of  nature.  Nevertheless,  most  or  all  of  these 
plants  retain  structures  in  an  efficient  state  which 
cannot  be  of  the  least  use  excepting  for  cross- 
fertilisation.  We  have  also  seen  reason  to  suspect 
that  self-fertilisation  is  in  some  peculiar  manner  bene- 
ficial to  certain  plants  ;  but  if  this  be  really  the  case, 
the  benefit  thus  derived  is  far  more  than  counter- 
balanced by  a  cross  with  a  fresh  stock  or  with  a 
slightly  different  variety. 

Notwithstanding  the  several  considerations  just 
advanced,  it  seems  to  me  highly  improbable  that 
plants  bearing  small  and  inconspicuous  flowers  have 
been  or  should  continue  to  be  subjected  to  self- 
fertilisation  for  a  long  series  of  generations.  I  think 
so,  not  from  the  evil  which  manifestly  follows  from 
self-fertilisation,  in  many  cases  even  in  the  first  gene- 
ration, as  with  Viola  tricolor,  Sarothamnus,  Nemo- 
phila,  Cyclamen,  &c. ;  nor  from  the  probability  of  the 
evil  increasing  after  several  generations,  for  on  this 
latter  head  I  have  not  sufficient  evidence,  owing  to  the 
manner  in  which  my  experiments  were  conducted.  But 
if  plants  bearing  small  and  inconspicuous  flowers  were 
not  occasionally  intercrossed,  and  did  not  profit  by  the 
process,  all  their  flowers  would  probably  have  been 
rendered  cleistogene,  as  they  would  thus  have  largely 
benefited  by  having  to  produce  only  a  small  quantity 
of  safely-protected  pollen.  In  coming  to  this  con- 
clusion, I  have  been  guided  by  the  frequency  with 
which  plants  belonging  to  distinct  orders  have  been 
rendered  cleistogene.  But  I  can  hear  of  no  instance 
of  a  species  with  all  its  flowers  rendered  permanently 


Chap.  X.  INCONSPICUOUS  FLOWEES.  387 

cleistogene.  Leersia  makes  the  nearest  approach  to 
this  state ;  but  as  already  stated,  it  has  been  known 
to  produce  perfect  flowers  in  one  part  of  Germany. 
Some  other  plants  of  the  cleistogene  class,  for  instance 
Aspicarpa,  have  failed  to  produce  perfect  flowers  during 
several  years  in  a  hothouse  ;  but  it  does  not  follow  that 
they  would  fail  to  do  so  in  their  native  country,  any 
more  than  with  Vandellia,  which  with  me  produced 
only  cleistogene  flowers  during  certain  years.  Plants 
belonging  to  this  class  commonly  bear  both  kinds  of 
flowers  every  season,  and  the  perfect  flowers  of  Viola 
canina  yield  fine  capsules,  but  only  when  visited  by 
bees.  We  have  also  seen  that  the  seedlings  of  Ononis 
minutissima,  raised  from  the  perfect  flowers  fertilised 
with  pollen  from  another  plant,  were  finer  than  those 
from  self-fertilised  flowers ;  and  this  was  likewise  the 
case  to  a  certain  extent  with  Vandellia.  As  therefore 
no  species  which  at  one  time  bore  small  and  incon- 
spicuous flowers  has  had  all  its  flowers  rendered 
cleistogene,  I  must  believe  that  plants  now  bearing 
small  and  inconspicuous  flowers  profit  by  their  still 
remaining  open,  so  as  to  be  occasionally  intercrossed 
by  insects.  It  has  been  one  of  the  greatest  oversights 
in  my  work  that  I  did  not  experimentise  on  such 
flowers,  owing  to  the  difficulty  of  fertilising  them,  and 
to  my  not  having  seen  the  importance  of  the  subject.* 


*  Some  of  the  species  of  Sola-  num)  do  not  intercross  when  they 

num.  would  be  good  ones  for  such  are  cultivated  near  totr<  ther ;  but 

experiments,  for  tliey  are  said  by  it    should   be    remembered    that 

H.  Miiller  ('  Befruchtung/  p.  434)  these    are    not   en  lemic   species, 

to  be  unattractive  to  injects  from  On  the  other  haul,  the  flowers  of 

not  secreting  nectar, not  producing  the  common  potato  (S.  tuberosum), 

n.uch  pollen,  ami  not  h  ing  very  though  they  do  not  secrete  nectar 

conspicuous.      Hence  probably  it  (Kurr,    '  Bedeutuug   der    Nekta- 

is  that,  according  to  Verlot  t/ Pro-  rien,'  1833,  p.  40),  yet  cannot  be 

ductimi  cl  s  Varietes,'  1*65,  p.  7'2),  cousideied  as  inconspicuous,  aud 

the  varieties  of   "  les  aubergines  they   are    sometimes    visited    by 

et  les  tomates"  (species  of  Sola-  Diptera  (Miiller)  and,  as  I  have 


388  MEANS   OF   CEOSS-FEKTILISATTON.         Chap.  X. 

It  should  be  remembered  that  in  two  of  the  cases  in 
which  highly  self-fertile  varieties  appeared  amongst 
my  experimental  plants,  namely,  with  Mimulus  and 
Nicotiana,  such  varieties  were  greatly  benefited  by  a 
cross  with  a  fresh  stock  or  with  a  slightly  different 
variety ;  and  this  likewise  was  the  case  with  the 
cultivated  varieties  of  Pisum  sativum  and  Lathyrus 
odoratus,  which  have  been  long  propagated  by  self- 
fertilisation.  Therefore  until  the  contrary  is  distinctly 
proved,  I  must  believe  that  as  a  general  rule  small  and 
inconspicuous  flowers  are  occasionally  intercrossed  by 
insects ;  and  that  after  long-continued  self-fertilisation, 
if  they  are  crossed  with  pollen  brought  from  a  plant 
growing  under  somewhat  different  conditions,  or 
descended  from  one  thus  growing,  their  offspring 
would  profit  greatly.  It  cannot  be  admitted,  under 
our  present  state  of  knowledge,  that  self-fertilisation 
continued  during  many  successive  generations  is  ever 
the  most  beneficial  method  of  reproduction. 

The  Means  which  favour  or  ensure  Floivers  being  fer- 
tilised with  Pollen  from  a  distinct-  Plant. — We  have  seen 
in  four  cases  that  seedlings  raised  from  a  cross  between 
flowers  on  the  same  plant,  even  on  plants  appearing 
distinct  from  having  been  propagated  by  stolons  or  cut- 
tings, were  not  superior  to  seedlings  from  self-fertilised 
flowers;  and  in  a  fifth  case  (Digitalis)  superior  only 
in  a  slight  degree.  Therefore  we  might  expect  that 
with  plants  growing  in  a  state  of  nature  a  cross  between 
the  flowers  on  distinct  individuals,  and  not  merely 
between  the  flowers  on  the  same  plant,  would  generally 


seen,     by    humble-bees.       Tinz-  bear  seed  when    fertilised  with 

mann  (as  quoted  in  'Gardeners'  pollen  from  the  same  variety,  but 

Chronicle,'   1846,   p.   183)   fouud  were  fertile  with  that  from  an* 

that  some  of  the  varieties  did  not  other  variety. 


Chap.  X.  MEANS   OF   CROSS-FERTILISATION".  389 

or  often  be  effected  by  some  means.  The  fact  of  bees 
and  of  some  Diptera  visiting  the  flowers  of  the  same 
species  as  long  as  they  can,  instead  of  promiscuously 
visiting  various  species,  favours  the  intercrossing  of 
distinct  plants.  On  the  other  hand,  insects  usually 
search  a  large  number  of  flowers  on  the  same  plant 
before  they  fly  to  another,  and  this  is  opposed  to  cross- 
fertilisation.  The  extraordinary  number  of  flowers 
which  bees  are  able  to  search  within  a  very  short  space 
of  time,  as  will  be  shown  in  a  future  chapter,  increases 
the  chance  of  cross-fertilisation ;  as  does  the  fact 
that  they  are  not  able  to  perceive  without  entering  a 
flower  whether  other  bees  have  exhausted  the  nectar. 
For  instance,  H.  Muller  found*  that  four-fifths  of  the 
flowers  of  Lamium  album  which  a  humble-bee  visited 
had  been  already  exhausted  of  their  nectar.  In  order 
that  distinct  plants  should  be  intercrossed,  it  is  of  course 
indispensable  that  two  or  more  individuals  should  grow 
near  one  another  ;  and  this  is  generally  the  case.  Thus 
A.  do  Candolle  remarks  that  in  ascending  a  mountain 
the  individuals  of  the  same  species  do  not  commonly 
disappear  near  its  upper  limit  quite  gradually,  but 
rather  abruptly.  This  fact  can  hardly  be  explained 
by  the  nature  of  the  conditions,  as  these  graduate  away 
in  an  insensible  manner,  and  it  probably  depends  in 
large  part  on  vigorous  seedlings  being  produced  only 
as  high  up  the  mountain  as  many  individuals  can 
subsist  together. 

With  respect  to  dicecious  plants,  distinct  individuals 
must  always  fertilise  each  other.  With  monoecious 
plants,  as  pollen  has  to  be  carried  from  flower  to  flower, 
there  will  always  be  a  good  chance  of  its  being  carried 
from  plant  to  plant.     Delpino  has  also  observed  f  the 

*   '  Die    Befruclitung,'   &c.    p.  t  '  Ult.  Osservazioni,'  &c,  part 

311,  ii.  fasc.  ii.  p.  337. 


390  MEANS   OF   CROSS-FEETILISATION.         Chap.  X. 

curious  fact  that  certain  individuals  of  trie  monoecious 
walnut  (Juglans  regia)  are  proterandrous,  and  others 
proterogynous,  and  these  will  reciprocally  fertilise  each 
other.  So  it  is  with  the  common  nut  (Corylus  avellana),  * 
and,  what  is  more  surprising,  with  some  few  her- 
maphrodite plants,  as  observed  by  H.  Miiller.t  These 
latter  plants  cannot  fail  to  act  on  each  other  like 
dimorphic  or  trimorphic  species,  in  which  the  union 
of  two  individuals  is  necessary  for  full  and  normal 
fertility.  With  ordinary  hermaphrodite  species,  the 
expansion  of  only  a  few  flowers  at  the  same  time  is  one 
of  the  simplest  means  for  favouring  the  intercrossing  of 
distinct  individuals ;  but  this  would  render  the  plants 
less  conspicuous  to  insects,  unless  the  flowers  were  of 
large  size,  as  in  the  case  of  several  bulbous  plants. 
Kerner  thinks  %  that  it  is  for  this  object  that  the 
Australian  Villarsia  parnassifolia  produces  daily  only 
a  single  flower.  Mr.  Cheeseman  also  remarks,§  that 
as  certain  Orchids  in  New  Zealand  which  require 
insect-aid  for  their  fertilisation  bear  only  a  single 
flower,  distinct  plants  cannot  fail  to  intercross. 

Dichogamy,  which  prevails  so  extensively  throughout 
the  vegetable  kingdom,  much  increases  the  chance  of 
distinct  individuals  intercrossing.  With  proterandrous 
species,  which  are  far  more  common  than  pro- 
terogynous, the  young  flowers  are  exclusively  male 
in  function,  and  the  older  ones  exclusively  female ; 
and  as  bees  habitually  alight  low  down  on  the  spikes 
of  flowers  in  order  to  crawl  upwards,  they  get  dusted 
with  pollen  from  the  uppermost  flowers,  which  they 
carry  to  the  stigmas  of  the  lower  and  older  flowers 
on  the  next  spike  which  they  visit.     The  degree  to 


*  '  Nature,'  1875,  p.  26.  J  'Die  S<-hutzmittel,'  &c.  p.  23 

t  '  Die   Befrucktung,'   &c.   pp.  §  '  Transact.   New  Zealand  In- 

2S5,  339.  stitut,e,'  vol.  v.  1873,  p.  356. 


y 


Chap.  X.         PEEPOTENT  POLLEN.  391 

which  distinct  plants  will  thus  be  intercrossed  depends 
on  the  number  of  spikes  in  full  flower  at  the  same  time 
on  the  same  plant.  With  proterogynous  flowers  and 
with  depending  racemes,  the  manner  in  which  insects 
visit  the  flowers  ought  to  be  reversed  in  order  that 
distinct  plants  should  be  intercrossed.  But  this  whole 
subject  requires  further  investigation,  as  the  great 
importance  of  crosses  between  distinct  individuals, 
instead  of  merely  between  distinct  flowers,  has  hitherto 
been  hardly  recognised. 

In  some  few  cases  the  special  movements  of  certain 
organs  almost  ensure  pollen  being  carried  from  plant 
to  plant.  Thus  with  many  orchids,  the  pollen-masses 
after  becoming  attached  to  the  head  or  proboscis  of  an 
insect  do  not  move  into  the  proper  position  for  striking 
the  stigma,  until  ample  time  has  elapsed  for  the  insect 
to  fly  to  another  plant.  With  Sjriranthes  autumnalis, 
the  pollen-masses  cannot  be  applied  to  the  stigma  until 
the  labellum  and  rostellum  have  moved  apart,  and 
this  movement  is  very  slow.*  With  Posoqueria  fra- 
grans  (one  of  the  Rubiaceffi)  the  same  end  is  gained  by 
the  movement  of  a  specially  constructed  stamen,  as 
described  by  Fritz  Muller. 

We  now  come  to  a  far  more  general  and  therefore 
more  important  means  by  which  the  mutual  fertilisation 
of  distinct  plants  is  effected,  namely,  the  fertilising 
power  of  pollen  from  another  variety  or  individual 
being  greater  than  that  of  a  plant's  own  pollen.  The 
simplest  and  best  known  case  of  prepotent  action 
in  pollen,  though  it  does  not  bear  directly  on  our 
present  subject,  is  that  of  a  plant's  own  pollen  over  that 
from  a  distinct  species.  If  pollen  from  a  distinct  species 
be  placed  on  the  stigma  of  a  castrated  flower,  and  then 

*  '  The  Various  Contrivances  Orchids  are  fertilised,'  1st  edit 
jy  which    Lri.iah    and    Foreign      p.  128. 


392  MEANS   OF  CKOSS-FEKTILISATION.  Chap.  X. 

after  the  interval  of  several  hours,  pollen  from  the  same 
species  be  placed  on  the  stigma,  the  effects  of  the 
former  are  wholly  obliterated,  excepting  in  some  rare 
cases.  If  two  varieties  are  treated  in  the  same  manner, 
the  result  is  analogous,  though  of  directly  opposite 
nature ;  for  pollen  from  any  other  variety  is  often  or 
generally  prepotent  over  that  from  the  same  flower.  I 
will  give  some  instances :  the  pollen  of  Mimulus  luteus 
regularly  falls  on  the  stigma  of  its  own  flower,  for  the 
plant  is  highly  fertile  when  insects  are  excluded.  Now 
several  flowers  on  a  remarkably  constant  whitish  variety 
were  fertilised  without  being  castrated  with  pollen  from 
a  yellowish  variety  ;  and  of  the  twenty-eight  seedlings 
thus  raised,  every  one  bore  yellowish  flowers,  so  that 
the  pollen  of  the  yellow  variety  completely  overwhelmed 
that  of  the  mother-plant.  Again,  Iberis  umbellata  is 
spontaneously  self-fertile,  and  I  saw  an  abundance  of 
pollen  from  their  own  flowers  on  the  stigmas ;  neverthe- 
less, of  thirty  seedlings  raised  from  non-castrated  flowers 
of  a  crimson  variety  crossed  with  pollen  from  a  pink 
variety,  twenty-four  bore  pink  flowers,  like  those  of  the 
male  or  pollen-bearing  parent. 

In  these  two  cases  flowers  were  fertilised  with  pollen 
from  a  distinct  variety,  and  this  was  shown  to  be 
prepotent  by  the  character  of  the  offspring.  Nearly 
similar  results  often  follow  when  two  or  more  self-fertile 
varieties  are  allowed  to  grow  near  one  another  and  are 
visited  by  insects.  The  common  cabbage  produces  a 
large  number  of  flowers  on  the  same  stalk,  and  when 
insects  are  excluded  these  set  many  capsules,  moderately 
rich  in  seeds.  I  planted  a  white  Kohl-rabi,  a  purple 
Kohl-rabi,  a  Portsmouth  broccoli,  a  Brussels  sprout, 
and  a  Sugar-loaf  cabbage  near  together  and  left  them 
uncovered.  Seeds  collected  from  each  kind  were  sown 
in  separate  beds ;  and  the  majority  of  the  seedlings  in 


Chap.  X.         PKEPOTENT  POLLEN.  393 

all  five  beds  were  mongrelisecl  in  the  most  complicated 
manner,  some  taking  more  after  one  variety,  and  some 
after  another.  The  effects  of  the  Kohl-rabi  were 
particularly  plain  in  the  enlarged  stems  of  many  of  the 
seedlings.  Altogether  233  plants  were  raised,  of  which 
155  were  mongrelised  in  the  plainest  manner,  and  of 
the  remaining  78  not  half  were  absolutely  pure.  I 
repeated  the  experiment  by  planting  near  together 
two  varieties  of  cabbage  with  purple-green  and  white- 
green  lacinated  leaves;  and  of  the  325  seedlings 
raised  from  the  purple-green  variety,  165  had  white- 
green  and  160  purpie-green  leaves.  Of  the  466  seed- 
lings raised  from  the  white-green  variety,  220  had 
purple-green  and  246  white-green  leaves.  These  cases 
show  how  largely  pollen  from  a  neighbouring  variety 
of  the  cabbage  effaces  the  action  of  the  plant's  own 
pollen.  We  should  bear  in  mind  that  pollen  must  be 
carried  by  the  bees  from  flower  to  flower  on  the  same 
large  branching  stem  much  more  abundantly  than 
from  plant  to  plant ;  and  in  the  case  of  plants  the 
flowers  of  which  are  in  some  degree  dichogamous, 
those  on  the  same  stem  would  be  of  different  ages,  and 
would  thus  be  as  ready  for  mutual  fertilisation  as  the 
flowers  on  distinct  plants,  were  it  not  for  the  prepotency 
of  pollen  from  another  variety.* 

Several  varieties  of  the  radish  (Baphanus  sativus), 
which  is  moderately  self-fertile  when  insects  are  ex- 
cluded, were  in  flower  at  the  same  time  in  my  garden. 
Seed  was  collected  from  one  of  them,  and  out  of  twenty- 
two  seedlings  thus  raised  only  twelve  were  true  to  their 
kind.f  [ 

*  A  writer  in  the  'Gardeners'  the    seeds    of   the  former.     The 
Chronicle'    (1855,    p.   730)    says  result  was  that  scarcely  one  seed- 
that  he  planted  a  hed  of  turnips  ling   was  true   to   its  kind,   and 
(Brassica  rapa)  and  of  rape   {£.  several  closely  resembled  rape. 
napus)  close  together,  and  sowed  f  Duhamel,  as  quoted  by  God* 


394  MEANS   OF   CROSS-FEETILISATION.  Chap.X. 

The  onion  produces  a  large  number  of  flowers,  all 
crowded  together  into  a  large  globular  head,  each 
flower  having  six  stamens ;  so  that  the  stigmas  receive 
plenty  of  pollen  from  their  own  and  the  adjoining 
anthers.  Consequently  the  plant  is  fairly  self- fertile 
when  protected  from  insects.  A  blood-red,  silver, 
globe  and  Spanish  onion  were  planted  near  together ; 
and  seedlings  were  raised  from  each  kind  in  four 
separate  beds.  In  all  the  beds  mongrels  of  various 
kinds  were  numerous,  except  amongst  the  ten  seedlings 
from  the  blood-red  onion,  which  included  only  two. 
Altogether  forty-six  seedlings  were  raised,  of  which 
thirty-one  had  been  plainly  crossed. 

A  similar  result  is  known  to  follow  with  the  varieties 
of  many  other  plants,  if  allowed  to  flower  near  together  : 
I  refer  here  only  to  species  which  are  capable  of 
fertilising  themselves,  for  if  this  be  not  the  case,  they 
would  of  course  be  liable  to  be  crossed  by  any  other 
variety  growing  near.  Horticulturists  do  not  commonly 
distinguish  between  the  effects  of  variability  and  inter- 
crossing ;  but  I  have  collected  evidence  on  the  natural 
crossing  of  varieties  of  the  tulip,  hyacinth,  anemone, 
ranunculus,  strawberry,  Leptosiphon  androsaceus,  orange 
rhododendron  and  rhubarb,  all  of  which  plants  I  believe 
to  be  self-fertile.*     Much  other  indirect  evidence  could 


ron,  '  De  l'Espece,'  torn.  ii.  p.  50,  have  myself  known  extensive 
makes  an  analogous  statement  crossing  to  occur  with  the  common 
with  respect  to  this  plant.  rhubarb.  For  Leptosiphon,  Verlot, 
*  With  respect  to  tulips  and  '  Des  Varie'te's,'  1865,  p.  20.  I  have 
some  other  flowers,  see  Godron,  not  included  in  my  list  the  Car- 
'De  I'lvspece,' torn.  i.  p.  252.  For  nation,  Nem<>phila,  or  Antir- 
ancm<>nes,  '  Gard.  Chron.'  1S59,  rliinum,  the  varieties  of  which  are 
p  98.  For  strawberries,  see  Her-  known  to  cross  freely,  because 
bert  in  'Transact,  of  Hort.  Soc'  these  plants  are  not  always  self- 
vol.  iv.  p.  17.  The  same  observer  fertile.  I  know  nothing  about 
elsewhere  speaks  of  the  sponta-  the  self-fertility  of  Trollins  (Le- 
mons crossing  of  rhododendions.  coq,  '  De  la  Fe'condntion,'  1862, 
.  Gallesio  makes  the  same  state-  p.  93),  Mahonia,  and  Crinum,  in 
incut  with  respect  to  oranges.     I  which  genera  the  species  intercross 


Chap  X.  PREPOTENT  POLLEN.  395 

be  given  with  respect  to  the  extent  to  which  varieties 
of  the  same  species  spontaneously  intercross. 

Gardeners  who  raise  seed  for  sale  are  compelled  by 
dearly  bought  experience  to  take  extraordinary  pre- 
cautions against  intercrossing.  Thus  Messrs.  Sharp 
"  have  land  engaged  in  the  growth  of  seed  in  no  less 
than  eight  parishes."  The  mere  fact  of  a  vast  number 
of  plants  belonging  to  the  same  variety  growing 
together  is  a  considerable  protection,  as  the  chances 
are  strong  in  favour  of  plants  of  the  same  variety  inter- 
crossing ;  and  it  is  in  chief  part  owing  to  this  circum- 
stance, that  certain  villages  have  become  famous  for 
pure  seed  of  particular  varieties.*  Only  two  trials 
were  made  by  me  to  ascertain  after  how  long  an  interval 
of  time,  pollen  from  a  distinct  variety  would  obliterate 
more  or  less  completely  the  action  of  a  plant's  own 
pollen.  The  stigmas  in  two  lately  expanded  flowers  on 
a  variety  of  cabbage,  called  Bagged  Jack,  were  well 
covered  with  pollen  from  the  same  plant.  After  an 
interval  of  twenty-three  hours,  pollen  from  the  Early 
Barnes  Cabbage  growing  at  a  distance  was  placed  on 
both  stigmas;  and  as  the  plant  was  left  uncovered, 
pollen  from  other  flowers  on  the  Eagged  Jack  would 
certainly  have  been  left  by  the  bees  during  the  next 
two  or  three  days  on  the  same  two  stigmas.  Under 
these  circumstances  it  seemed  very  unlikely  that  the 
pollen  of  the  Barnes  cabbage  would  produce  any  effect ; 
but  three  out  of  the  fifteen  plants  raised  from  the  two 
capsules  thus  produced  were  plainly  mongrelised  :  and 
I  have  no  doubt  that  the  twelve  other  plants  were 

largely.   With  respect  to  Mahonia,  so  freely  that  pure  seed  could  not 

it  is  now  scarcely  possible  to  pro-  be  saved. 

cure  in  this  country  pure  speci-  *  With  respect  to  Messrs.  Sharp, 

mens  of  M.  aquifolimn  or  repens;  see  'Gardeners'  Chronicle,'  1856, 

and  the  various  species  of  Criuum  p.  823.   Lindley's '  Theory  of  Hor- 

sent  by  Herbert  ('  Amaryllidacese,'  ticulture,'  p.  319. 

p.  32)  to  Ca  cuttu,  crossed  there 


396  MEANS   OF   CROSS-FERTILISATION.  Chap.  X. 

affected,  for  they  grew  much  more  vigorously  than  the 
self-fertilised  seedlings  from  the  Eagged  Jack  planted 
at  the  same  time  and  under  the  same  conditions. 
Secondly,  I  placed  on  several  stigmas  of  a  long-styled 
cowslip  [Primula  veris)  plenty  of  pollen  from  the  same 
plant,  and  after  twenty-four  hours  added  some  from  a 
short-styled  dark-red  Polyanthus,  which  is  a  variety  of 
the  cowslip.  From  the  flowers  thus  treated  thirty 
seedlings  were  raised,  and  all  these  without  exception 
bore  reddish  flowers ;  so  that  the  effect  of  the  plant's 
own  pollen,  though  placed  on  the  stigmas  twenty- 
four  hours  previously,  was  quite  destroyed  by  that  of 
the  red  variety.  It  should,  however,  be  observed  that 
these  plants  are  dimorphic,  and  that  the  second  union 
was  a  legitimate  one,  whilst  the  first  was  illegitimate ; 
but  flowers  illegitimately  fertilised  with  their  own  pollen 
yield  a  moderately  fair  supply  of  seeds. 

We  have  hitherto  considered  only  the  prepotent 
fertilising  power  of  pollen  from  a  distinct  variety  over 
a  plant's  own  pollen, — both  kinds  of  pollen  being 
placed  on  the  same  stigma.  It  is  a  much  more  re- 
markable fact  that  pollen  from  another  individual  of 
the  same  variety  is  prepotent  over  a  plant's  own  pollen, 
as  shown  by  the  superiority  of  the  seedlings  raised 
from  a  cross  of  this  kind  over  seedlings  from  self- 
fertilised  flowers.  Thus  in  Tables  A,  B,  and  C,  there 
are  at  least  fifteen  species  which  are  self-fertile  when 
insects  are  excluded  ;  and  this  implies  that  their  stigmas 
must  receive  their  own  pollen  ;  nevertheless,  most  of 
the  seedlings  which  were  raised  by  fertilising  the  non- 
castrated  flowers  of  these  fifteen  species  with  pollen 
from  another  plant  were  greatly  superior,  in  height, 
weight,  and  fertility,  to  the  self-fertilised  offspring.* 


*  These  fifteen  species  consist  of      and  lutea,  Limnanthes  douglasii, 
Brassiea  oleracea,  Jtieseda  odorata       Palaver  vagum,  Yiscaria  oaulata, 


Ciiap.  X.  PKEPOTENT   POLLEN.  397 

For  instance,  with  Ipomoea  'purpurea  every  single  inter- 
crossed plant  exceeded  in  height  its  self-fertilised 
opponent  until  the  sixth  generation ;  and  so  it  was 
with  Mimulus  luteus  until  the  fourth  generation.  Out 
of  six  pairs  of  crossed  and  self-fertilised  cabbages,  every 
one  of  the  former  was  much  heavier  than  the  latter. 
With  Papaver  vagum,  out  of  fifteen  pairs,  all  but 
two  of  the  crossed  plants  were  taller  than  their  self- 
fertilised  opponents.  Of  eight  pairs  of  Lupinus  luteus, 
all  but  two  of  the  crossed  were  taller ;  of  eight  pairs 
of  Beta  vulgaris  all  but  one  ;  and  of  fifteen  pairs  of  Zea 
mays  all  but  two  were  taller.  Of  fifteen  pairs  of  Lim- 
nanthes  douglasii,  and  of  seven  pairs  of  Lactuca  sativa, 
every  single  crossed  plant  was  taller  than  its  self-fer- 
tilised opponent.  It  should  also  be  observed  that  in 
these  experiments  no  particular  care  was  taken  to  cross- 
fertilise  the  flowers  immediately  after  their  expansion ; 
it  is  therefore  almost  certain  that  in  many  of  these 
cases  some  pollen  from  the  same  flower  will  have 
already  fallen  on  and  acted  on  the  stigma. 

There  can  hardly  be  a  doubt  that  several  other 
species  of  which  the  crossed  seedlings  are  more 
vigorous  than  the  self -fertilised,  as  shown  in  Tables  A, 
B,  and  C,  besides  the  above  fifteen,  must  have  received 
their  own  pollen  and  that  from  another  plant  at  nearly 
the  same  time ;  and  if  so,  the  same  remarks  as  those 
just  given  are  applicable  to  them.  Scarcely  any  result 
from  my  experiments  has  surprised  me  so  much  as  this 
of  the  prepotency  of  pollen  from  a  distinct  individual 
over  each  plant's  own  pollen,  as  proved  by  the  greater 
constitutional  vigour  of  the  crossed  seedlings.  The 
evidence   of  prepotency   is   here   deduced   from    the 


Beta    vulgaris,    Lupinus     luteus,       Vandellia    nummularifolia,   Lno- 
Ipnmaa  purpurea,  Mimulus  luteus,       tuca  sativa,  and  Zea  mays. 
Calceolaria,    Verbascum    thapsus, 


398  MEANS   OF   CROSS-FERTILISATION.  Chap.  X. 

comparative  growth  of  the  two  lots  of  seedlings ;  but 
we  have  similar  evidence  in  many  cases  from  the 
much  greater  fertility  of  the  non-castrated  flowers  on 
the  mother-plant,  when  these  received  at  the  same  time 
their  own  pollen  and  that  from  a  distinct  plant,  in 
comparison  with  the  flowers  which  received  only  their 
own  pollen. 

From  the  various  facts  now  given  on  the  spontaneous 
intercrossing  of  varieties  growing  near  together,  and  on 
the  effects  of  cross-fertilising  flowers  which  are  self- 
fertile  and  have  not  been  castrated,  we  may  conclude 
that  pollen  brought  by  insects  or  by  the  wind  from 
a  distinct  plant  will  generally  prevent  the  action  of 
pollen  from  the  same  flower,  even  though  it  may  have 
been  applied  some  time  before;  and  thus  the  inter- 
crossing of  plants  in  a  state  of  nature  will  be  greatly 
favoured  or  ensured. 

The  case  of  a  great  tree  covered  with  innumerable 
hermaphrodite  flowers  seems  at  first  sight  strongly 
opposed  to  the  belief  in  the  frequency  of  intercrosses 
between  distinct  individuals.  The  flowers  which  grow 
on  the  opposite  sides  of  such  a  tree  will  have  been 
exposed  to  somewhat  different  conditions,  and  a  cross 
between  them  may  perhaps  be  in  some  degree  beneficial; 
but  it  is  not  probable  that  it  would  be  nearly  so  bene- 
ficial as  a  cross  between  flowers  on  distinct  trees,  as  we 
may  infer  from  the  inefficiency  of  pollen  taken  from 
plants  which  have  been  propagated  from  the  same 
stock,  though  growing  on  separate  roots.  The  number 
of  bees  which  frequent  certain  kinds  of  trees  when  in 
full  flower  is  very  great,  and  they  may  be  seen  flying 
from  tree  to  tree  more  frequently  than  might  have 
been  expected.  Nevertheless,  if  we  consider  how 
numerous  are  the  flowers,  for  instance,  on  a  horse- 
chestnut  or  lime-tree,  an  incomparably  larger  number 


Chap.  X.  PKEPOTENT   POLLEN".  3D9 

of  flowers  must  be  fertilised  by  pollen  brought  from 
other  flowers  on  the  same  tree,  than  from  flowers  on  a 
distinct  tree.     But  we  should  bear  in  mind  that  with 
the  horse-chestnut,  for  instance,  only  one  or  two  of  the 
several  flowers  on  the  same  peduncle  produce  a  seed ; 
and  that  this  seed  is  the  product  of  only  one  out  of 
several  ovules  within  the  same  ovarium.     Now  we  know 
from  the  experiments  of  Herbert  and  others*  that  if  one 
flower  is  fertilised  with  pollen  which  is  more  efficient 
than  that   applied  to  the  other  flowers  on  the  same 
peduncle,  the  latter  often  drop  off ;  and  it  is  probable 
that  this  would  occur  with  many  of  the  self-fertilised 
flowers  on  a  large  tree,  if  other  and  adjoining  flowers 
were  cross-fertilised.     Of  the  flowers  annually  produced 
by  a   great   tree,  it   is   almost   certain   that   a  large 
number  would   be   self-fertilised ;    and  if  we  assume 
that  the  tree  produced  only  500  flowers,  and  that  this 
number  of  seeds  were  requisite  to  keep  up  the  stock, 
so  that  at  least  one  seedling  should  hereafter  struggle 
to  maturity,  then  a  large  proportion  of  the  seedlings 
would  necessarily  be  derived  from  self-fertilised  seeds. 
But  if  the  tree  annually  produced  50,000  flowers,  of 
which  the  self-fertilised  dropped  off  without  yielding 
seeds,   then   the   cross-fertilised   flowers   might  yield 
seeds  in  sufficient  number  to  keep  up  the  stock,  and 
most  of  the  seedlings  would  be  vigorous  from  being 
the  product  of  a   cross  between  distinct  individuals. 
In  this  manner  the  production  of  a  vast  number  of 
flowers,  besides  serving  to  entice  numerous  insects  and 
to  compensate  for  the  accidental  destruction  of  many 
flowers  by  spring-frosts  or  otherwise,  would  be  a  very 
great  advantage  to  the  species ;  and  when  we  behold 
our  orchard-trees  covered  with  a  white  sheet  of  bloom 


1  Variation  under  Domestication,'  ch.  xvii.  2nd  edit.  vol.  ii.  p.  120. 
18 


100  ANEMOPHILOTJS  PLANTS.  Chap.  X. 

in  the  spring,  we  should  not  falsely  accuse  nature  of 
wasteful  expenditure,  though  comparatively  little  fruit 
is  produced  in  the  autumn. 

Anemophilous  Plants. — The  nature  and  relations  of 
plants  which  are  fertilised  by  the  wind  have  been 
admirably  discussed  by  Delpino*  and  H.  Muller ;  and 
I  have  already  made  some  remarks  on  the  structure  of 
their  flowers  in  contrast  with  those  of  entomophilous 
species.  There  is  good  reason  to  believe  that  the  first 
plants  which  appeared  on  this  earth  were  cryptogamic  ; 
and  judging  from  what  now  occurs,  the  male  fertilising 
element  must  either  have  possessed  the  power  of  spon- 
taneous movement  through  the  water  or  over  damp 
surfaces,  or  have  been  carried  by  currents  of  water  to 
the  female  organs.  That  some  of  the  most  ancient 
plants,  such  as  ferns,  possessed  true  sexual  organs  there 
can  hardly  be  a  doubt ;  and  this  shows,  as  Hildebrand 
remarks,!  at  how  early  a  period  the  sexes  were  separated. 
As  soon  as  plants  became  phanerogamic  and  grew  on 
the  dry  ground,  if  they  were  ever  to  intercross,  it  would 
be  indispensable  that  the  male  fertilising  element 
should  be  transported  by  some  means  through  the 
air ;  and  the  wind  is  the  simplest  means  of  transport. 
There  must  also  have  been  a  period  when  winged 
insects  did  not  exist,  and  plants  would  not  then  have  been 
rendered  entomophilous.  Even  at  a  somewhat  later 
period  the  more  specialised  orders  of  the  Hymenoptera, 


*  Delpino,    'Ult.  Osservazioni  further   discusses  in   a  very  in- 

sulla  Dicogamia,'  part  ii.  fasc.  i.  teresting  manner    Ihe  steps     by 

1870;  and  '  Studi  sopra  un  Lig-  which  entomophilous  flowers  be- 

naggio  anernofilo,'  &c.   1871.     H.  came  nectariferous  and  gradually 

Muller,  '  Die    Befruchtung,'    &c.  acquired   their  present  structure 

pp.  412,  442.     Both  the^e  authors  through      successive      beneficial 

remark   that   plants    must    have  changes. 

beeu    anemophilous    before  they  t  '  Die  Geschlechter-Yertheil- 

were   entomophilous.     H.  Muller  ung,'  1867,  pp.  84-90. 


Chap.  X.  ANEMOPHILOUS  PLANTS.  401 

Lepidoptera,  and  Diptera,  which,  are  now  chiefly  con- 
cerned with  the  transport  of  pollen,  did  not  exist. 
Therefore  the  earliest  terrestrial  plants  known  to  us, 
namely,  the  Coniferse  and  Cycadiae,  no  doubt  were  ane- 
mophilous,  like  the  existing  species  of  these  same 
groups.  A  vestige  of  this  early  state  of  things  is 
likewise  shown  by  some  other  groups  of  plants  which 
are  anemophilous,  as  these  on  the  whole  stand  lower 
in  the  scale  than  entomophilous  species. 

There  is  no  great  difficulty  in  understanding  how  an 
anemophilous  plant  might  have  been  rendered  entomo- 
philous. Pollen  is  a  nutritious  substance,  and  would 
soon  have  been  discovered  and  devoured  by  insects; 
and  if  any  adhered  to  their  bodies  it  would  have  been 
carried  from  the  anthers  to  the  stigma  of  the  same 
flower,  or  from  one  flower  to  another.  One  of  the  chief 
characteristics  of  the  pollen  of  anemophilous  plants 
is  its  incoherence ;  but  pollen  in  this  state  can  adhere 
to  the  hairy  bodies  of  insects,  as  we  see  with  some 
Leguminosee,  Ericaceae,  and  Melastomaceae.  We  have, 
however,  better  evidence  of  the  possibility  of  a  tran- 
sition of  the  above  kind  in  certain  plants  being  now 
fertilised  partly  by  the  wind  and  partly  by  insects. 
The  common  rhubarb  (Rheum  rhaponticum)  is  so  far 
in  an  intermediate  condition,  that  I  have  seen  many 
Diptera  sucking  the  flowers,  with  much  pollen  adhering 
to  their  bodies;  and  yet  the  pollen  is  so  incoherent, 
that  clouds  of  it  are  emitted  if  the  plant  be  gently 
shaken  on  a  sunny  day,  some  of  which  could  hardly 
fail  to  fall  on  the  large  stigmas  of  the  neighbouring 
flowers.  According  to  Delpino  and  H.  Miiller,*  some 
species  of  Plantago  are  in  a  similar  intermediate 
condition. 


*  'Die  Befruchtung,'  &o.  p.  342. 


102  ANEMOPHILOTJS   PLANTS.  Chap.  X. 

Although,  it  is  probable  that  pollen  was  aboriginally 
the  sole  attraction  to  insects,  and  although  many 
plants  now  exist  whose  flowers  are  frequented  exclu- 
sively by  pollen-devouring  insects,  yet  the  great 
majority  secrete  nectar  as  the  chief  attraction.  Many 
years  ago  I  suggested  that  primarily  the  saccharine 
matter  in  nectar  was  excreted*  as  a  waste  product  of 
chemical  changes  in  the  sap ;  and  that  when  the  ex- 
cretion happened  to  occur  within  the  envelopes  of  a 
flower,  it  was  utilised  for  the  important  object  of 
cross-fertilisation,  being  subsequently  much  increased 
in  quantity  and  stored  in  various  ways.  This  view 
is  rendered  probable  by  the  leaves  of  some  trees  ex- 
creting, under  certain  climatic  conditions,  without  the 
aid  of  special  glands,  a  sacchaiine  fluid,  often  called 
honey-dew.  This  is  the  case  with  the  leaves  of  the 
lime ;  for  although  some  authors  have  disputed  the 
fact,  a  most  capable  judge,  Br.  Maxwell  Masters, 
informs  me  that,  after  having  heard  the  discussions  on 
this  subject  before  the  Horticultural  Society,  he  feels 
10  doubt  on  this  head.  The  leaves,  as  well  as  the 
out  stems,  of  the  manna  ash  (Fraxinus  ornus)  secrete 
in  a  like  manner  saccharine  matter.f  According  to 
Treviranus,  so  do  the  upper  surfaces  of  the  leaves  of 
Garduus  arctioides  during  hot  weather.  Many  ana- 
logous facts  could  be  given.J  There  are,  however, 
a  considerable  number  of  plants  which  bear  small 
glands  §  on  their  leaves,  petioles,  phyllodia,  stipules, 

*     Nectar    -was    regarded    by  §  A  large  number  of  cases  are 

De   Candolle   and   Dunal   as   an  given   by  Delpino    in   the  'Bul- 

excrction,  as  stated  hy  Martinet  btino    Entomologico,'   Anno    vi. 

in'  Anna!  des  Sc.  Nat.'  1872,  torn.  1874.      To  these   may  be  added 

xiv.  p.  211.  those  given  in  my  text,  as  well 

t  '  Gard.  Chron.' 1S76,  p.  242.  as   the    excretion    of    saccharine 

t  Kurr,  '  Uiitersuchungen  uhi-r  matter   from    the   calyx    of   two 

die  Bedeutung    der    Nektarien.'  species  of  Iris,  and  from  the  brac» 

1833,  p.  115.  tea)  of  certain  Orchideae :  see  Kurr, 


Chap.  X. 


SECRETION   OF  NECTAR. 


403 


bracteee,  or  flower  peduncles,  or  on  the  outside  of  their 
calyx,  and  these  glands  secrete  minute  drops  of  a  sweet 
fluid,  which  is  eagerly  sought  by  sugar-loving  insects, 
such  as  ants,  hive-bees,  and  wasps.  In  the  case  of 
the  glands  on  the  stipules  of  Vicia  sativa,  the  excre- 
tion manifestly  depends  on  changes  in  the  sap,  con- 
sequent on  the  sun  shining  brightly  ;  for  I  repeatedly 
observed  that  as  soon  as  the  sun  was  hidden  behind 
clouds  the  secretion  ceased,  and  the  hive-bees  left  the 
field ;  but  as  soon-  as  the  sun  broke  out  again,  they 
returned  to  their  feast.*  I  have  observed  an  analogous 
fact  with  the  secretion  of  true  nectar  in  the  flowers  of 
Lobelia  erinus. 

Delpino,  however,  maintains  that  the  power  of 
secreting  a  sweet  fluid  by  any  extra- floral  organ  has 
been  in  every  case  specially  gained,  for  the  sake  of 
attracting  ants   and  wasps  as  defenders  of  the  plant 


'Bedeutung  der  Nektarien,'  1S33, 
pp.  25,  28.  Belt  also  refers  ('  Ni- 
caragua,' p.  224)  to  a  similar 
excretion  by  many  epiphytal  or- 
chids and  passion-flowers.  Mr. 
Roilgers  has  seen  much  neciar 
secreted  from  the  bases  of  the 
flower-peduncles  of  Vanilla.  Link 
says  that  the  only  example  of  a 
hypopetalous  nectary  known  to 
him  is  externally  at  the  base  of 
the  flowers  of  Chironiadecussata: 
see  '  Reports  on  Botany,  Ray  So- 
ciety,' 1846,  p.  355.  An  impor- 
tant memoir  bearing  on  this  sub- 
ject has  lately  appeared  by  Relnke 
('Gottingen  Nacnrichten,'  1873, 
p.  825),  who  shows  that  in  many 
plants  the  tips  of  the  serrations 
on  tlie  leaves  in  the  bud  bear 
glands  which  secrete  only  at  a 
very  early  age,  and  which  have 
the  same  morphological  structure 
as  true  nectar-secreting  glands. 
He  further  shows  that  the  n-ctar- 
seci^ting  glands   on   the  petioles 


of  Prunus  avium  are  not  deve- 
loped at  a  very  early  age,  yet 
wither  away  on  the  old  leaves. 
They  are  homologous  with  those 
on  the  serrations  of  the  blades  of 
the  same  leaves,  as  shown  by 
their  structure  and  by  transition- 
forms  ;  for  the  lowest  serrations 
on  the  blades  of  mo^t  of  the  leaves 
secrete  nectar  instead  of  resin 
(harz). 

*  I  published  a  brief  notice  of 
this  case  in  the  '  Gard.  Chronicle,' 
1855,  July  21,  p.  487,  and  after- 
wards made  further  observations. 
Besides  the  hive-he,  another 
species  of  bee,  a  moth,  ants,  and 
two  kinds  of  flies  sucked  the 
drops  of  fluid  on  the  stipules. 
The  larger  drops  tasted  sweet. 
The  hive-bees  never  even  looked 
at  the  flowers  which  were  open 
at  the  same  time;  whilst  two 
species  of  humble-bees  neglected 
the  stipules  and  visited  only  the 
flowers. 


404  ANEMOPHILOTJS   PLANTS.  Chap.  X. 

against  their  enemies ;  but  I  have  never  seen  any 
reason  to  believe  that  this  is  so  with  the  three  species 
observed  by  me,  namely,  Primus  laurocerasus,  Vicia 
sativa,  and  V.  faba.  No  plant  is  so  little  attacked  by 
enemies  of  any  kind  as  the  common  bracken-fern 
(Pteris  aquilina) ;  and  yet,  as  my  son  Francis  has 
discovered,  the  large  glands  at  the  bases  of  the  fronds, 
but  only  whilst  young,  excrete  much  sweetish  fluid, 
which  is  eagerly  sought  by  innumerable  ants,  chiefly 
belonging  to  Myrmica;  and  these  ants  certainly  do 
not  serve  as  a  protection  against  any  enemy.  Delpino 
argues  that  such  glands  ought  not  to  be  considered  as 
excretory,  because  if  they  were  so,  they  would  be 
present  in  every  species ;  but  I  cannot  see  much  force 
in  this  argument,  as  the  leaves  of  some  plants  excrete 
sugar  only  during  certain  states  of  the  weather.  That 
in  some  cases  the  secretion  serves  to  attract  insects  as 
defenders  of  the  plant,  and  may  have  been  developed 
to  a  high  degree  for  this  special  purpose,  I  have  not 
the  least  doubt,  from  the  observations  of  Delpino, 
and  more  especially  from  those  of  Mr.  Belt  on  Acacia 
sphterocephala,  and  on  passion-flowers.  This  acacia 
likewise  produces,  as  an  additional  attraction  to  ants, 
small  bodies  containing  much  oil  and  protoplasm,  and 
analogous  bodies  are  developed  by  a  Cecropia  for  the 
same  purpose,  as  described  by  Fritz  Miiller.* 

The  excretion  of  a  sweet  fluid  by  glands  seated 
outside  of  a  flower  is  rarely  utilised  as  a  means  for 
cross-fertilisation  by  the  aid  of  insects ;  but  this  occurs 
with  the  bracteae  of  the  Marcgraviacese,  as  the  late 


*  Mr.  Belt  has  given  a  most  cropia,  see  'Nature,'  1876, p.  304. 
interesting  account  ('  The  Natu-  My  son  Francis  has  described  the 
ralist  in  Nicaragua,'  1S74,  p.  21S)  microscopical  structure  and  deve- 
of  the  paramount  importance  of  lopment  of  these  wonderful  food- 
ants  as  defenders  of  the  above  bodies  in  a  paper  read  before  the 
Acacia.    With  respect  to  the  Ce-  Linnean  Society. 


Chap.  X.  QUANTITY   OF   POLLEN.  405 

Dr.  Criiger  informed  me  from  actual  observation  in  the 
West  Indies,  and  as  Delpino  infers  with  much  acuteness 
from  the  relative  position  of  the  several  parts  of  their 
flowers.*  Mr.  Farrer  has  also  shown  f  that  the  flowers 
of  Coronilla  are  curiously  modified,  so  that  bees  may 
fertilise  them  whilst  sucking  the  fluid  secreted  from 
the  outside  of  the  calyx.  It  further  appears  probable 
from  the  observations  of  Rev.  W.  A.  Leighton,  that  the 
fl  uid  so  abundantly  secreted  by  glands  on  the  phy llodia 
of  the  Australian  Acacia  magnijica,  which  stand  near 
the  flowers,  is  connected  with  their  fertilisation.! 

The  amount  of  pollen  produced  by  anemophilous 
plants,  and  the  distance  to  which  it  is  often  trans- 
ported by  the  wind,  are  both  surprisingly  great.  Mr. 
Hassall  found  that  the  weight  of  pollen  produced  by  a 
single  plant  of  the  bulrush  (Typha)  was  144  grains. 
Bucketfuls  of  pollen,  chiefly  of  Coniferee  and  Gra- 
mmes, have  been  swept  off  the  decks  of  vessels  near 
the  North  American  shore ;  and  Mr.  Eiley  has  seen 
the  ground  near  St.  Louis,  in  Missouri,  covered  with 
pollen,  as  if  sprinkled  with  sulphur ;  and  there  was 
good  reason  to  believe  that  this  had  been  transported 
from  the  pine-forests  at  least  400  miles  to  the  south. 
Kerner  has  seen  the  snow-fields  on  the  higher  Alps 


*  'Ult.  Osservaz.  Dicogamia,'  spaces.  I  further  suggested,  in 
1868-69,  p.  188.  the  case  of  some  other  orchids 
f  '  Nature,'  1S74,  p.  169.  which  do  not  secrete  nectar,  that 
%  'Annals  and  Mag.  of  Nat.  insects  gnawed  the  labellum;  and 
Hist.'  vol.  xvi.  1865,  p.  14.  In  this  suggestion  lias  since  been 
my  work  on  the  'Fertilisation  of  proved  true.  H.  Miiller  and  Del- 
Orchid*,'  and  in  a  paper  subse-  pino  have  now  shown  that  some 
quently  published  in  the  '  Annals  other  plants  have  thickened  pe- 
and  Mag.  of  Nat.  History,"  it  has  tals  which  are  sacked  or  gnawed 
been  shown  that  although  certain  by  insects,  their  fertilisation  bt-ing 
kinds  of  orchids  possess  a  nectary,  thus  aided.  All  the  known  facts 
no  nectar  is  actually  secreted  by  on  this  head  have  been  collected 
it ;  but  that  insects  penetrate  the  by  Delpino  in  his  '  Ult.  Osserv. 
inner  walls  and  suck  the  fluid  part  ii.  fasc.  ii.  1875,  pp.  59-63. 
contained    in    the    intercellular 


406  ANEMOPHILOUS   PLANTS.  Chap.  X. 

similarly  dusted ;  and  Mr.  Blackley  found  numerous 
pollen-grains,  in  one  instance  1200,  adhering  to 
sticky  slides,  which  were  sent  up  to  a  height  of  from 
500  to  1000  feet  by  means  of  a  kite,  and  then  un- 
covered by  a  special  mechanism.  It  is  remarkable 
that  in  these  experiments  there  were  on  an  average 
nineteen  times  as  many  pollen-grains  in  the  atmosphere 
at  the  higher  than  at  the  lower  levels.*  Considering 
these  facts,  it  is  not  so  surprising  as  it  at  first  appears 
that  all,  or  nearly  all,  the  stigmas  of  anemophilous 
plants  should  receive  pollen  brought  to  them  by  mere 
chance  by  the  wind.  During  the  early  part  of  summer 
every  object  is  thus  dusted  with  pollen ;  for  instance, 
I  examined  for  another  purpose  the  labella  of  a  large 
number  of  flowers  of  the  Fly  Ophrys  (which  is  rarely 
visited  by  insects),  and  found  on  all  very  many  pollen- 
grains  of  other  plants,  which  had  been  caught  by  their 
velvety  surfaces. 

The  extraordinary  quantity  and  lightness  of  the 
pollen  of  anemophilous  plants  are  no  doubt  both 
necessary,  as  their  pollen  has  generally  to  be  carried 
to  the  stigmas  of  other  and  often  distant  flowers  ;  for, 
as  we  shall  soon  see,  most  anemophilous  plants  have 
their  sexes  separated.  The  fertilisation  of  these  plants 
is  generally  aided  by  the  stigmas  being  of  large 
size  or  plumose ;  and  in  the  case  of  the  Coniferse, 
by  the  naked  ovules  secreting  a  drop  of  fluid,  as 
shown   by  Delpino.      Although  the  number   of  ane- 

*  For  Mr.   Hassall's    observa-  Kerner,    'Die    Schutzmittel  des 

tions  see   'Annals  and   Mag.  of  Pollens,'  1X73,  p.  6.    This  author 

Nat.  Hist.'  vol.  viii.  1842,  p.  108.  has  also  seen  a  lake  in  the  Tyrol 

In  the  '  North  American  Journal  so  covered  with  pollen,  that  the 

of  Science,'  Jan.  1842,  there  is  an  water  no  longer  apjjeared   blue, 

account  of  the  pollen  swept  off  Mr.  Blackley,  ' Experimental  Ke- 

the    decks  of  a  vessel.      Riley,  searches     on     Hay-fever,'    1873, 

'  Fifth   Report  on    the    Noxious  pp.  lo2,  141-152. 
Insects  of  Missouri,'  1873,  p.  86. 


Chap.  X.  QUANTITY  OF  POLLEN.  407 

inophilous  species  is  small,  as  the  author  just  quoted 
remarks,  the  number  of  individuals  is  large  in  com- 
parison with  that  of  entomophilous  species.  This 
holds  good  especially  in  cold  and  temperate  regions, 
where  insects  are  not  so  numerous  as  under  a  warmer 
climate,  and  where  consequently  entomophilous  plants 
are  less  favourably  situated.  We  see  this  in  our 
forests  of  Coniferse  and  other  trees,  such  as  oaks, 
beeches,  birches,  ashes,  &c. ;  and  in  the  Graminese, 
Cyperacese,  and  Juncacese,  which  clothe  our  meadows 
and  swamps  ;  all  these  trees  and  plants  being  fertilised 
by  the  wind.  As  a  large  quantity  of  pollen  is  wasted 
by  anemophilous  plants,  it  is  surprising  that  so  many 
vigorous  species  of  this  kind  abounding  with  individuals 
should  still  exist  in  any  part  of  the  world  ;  for  if  they 
had  been  rendered  entomophilous,  their  pollen  would 
have  been  transported  by  the  aid  of  the  senses  and 
appetites  of  insects  with  incomparably  greater  safety 
than  by  the  wind.  That  such  a  conversion  is  possible 
can  hardly  be  doubted,  from  the  remarks  lately  made 
on  the  existence  of  intermediate  forms ;  and  apparently 
it  has  been  effected  in  the  group  of  willows,  as  we  may 
infer  from  the  nature  of  their  nearest  allies.* 

It  seems  at  first  sight  a  still  more  surprising  fact 
that  plants,  after  having  been  once  rendered  entomo- 
philous, should  ever  again  have  become  anemophilous  ; 
but  this  has  occasionally  though  rarely  occurred,  for 
instance,  with  the  common  Poterium  sanguisorba ,  as  may 
be  inferred  from  its  belonging  to  the  Rosaceae.  Such 
cases  are,  however,  intelligible,  as  almost  all  plants 
require  to  be  occasionally  intercrossed ;  and  if  any 
entomophilous  species  ceased  to  be  visited  by  insects, 
it    would    probably   perish    unless    it   were   rendered 


*  H.  Miiller,  'Die  Befruchtuug,'  &c.  p.  149, 


i08  SEXUAL   RELATIONS   OF   PLANTS.  Chap.  X. 

aneinophilous.  A  plant  would  be  neglected  by  insects 
if  nectar  failed  to  be  secreted,  unless  indeed  a  large 
supply  of  attractive  pollen  was  present;  and  from 
what  we  have  seen  of  the  excretion  of  saccharine  fluid 
from  leaves  and  glands  being  largely  governed  in 
several  cases  by  climatic  influences,  and  from  some 
few  flowers  which  do  not  now  secrete  nectar  still 
retaining  coloured  guiding-marks,  the  failure  of  the 
secretion  cannot  be  considered  as  a  very  improbable 
event.  The  same  result  would  follow  to  a  certainty, 
if  winged  insects  ceased  to  exist  in  any  district,  or 
became  very  rare.  Now  there  is  only  a  single 
plant  in  the  great  order  of  the  Cruciferae,  namely, 
Pringlea,  which  is  anemophilous,  and  this  plant  is 
an  inhabitant  of  Kerguelen  Land,*  where  there 
are  hardly  any  winged  insects,  owing  probably,  as 
was  suggested  by  me  in  the  case  of  Madeira,  to 
the  risk  which  they  run  of  being  blown  out  to  sea  and 
destroyed. 

A  remarkable  fact  with  respect  to  anemophilous 
plants  is  that  they  are  often  diclinous,  that  is,  they  are 
either  monoecious  with  their  sexes  separated  on  the 
same  plant,  or  dioecious  with  their  sexes  on  distinct 
plants.  In  the  class  Monoecia  of  Linnseus,  Delpino 
shows  f  that  the  species  of  twenty-eight  genera  are 
anemophilous,  and  of  seventeen  genera  entomophilous. 
In  the  class  Dioecia,  the  species  of  ten  genera  are 
anemophilous  and  of  nineteen  entomophilous.  The 
larger  proportion  of  entomophilous  genera  in  this 
latter  class  is  probably  the  indirect  result  of  insects 
having  the  power  of  carrying  pollen  to  another  and 
sometimes  distant  plant  much  more  securely  than  the 


*  The    Rev.   A.   E.   Eaton  in  f  'Studi  sopra   un   Lignaggio 

'  Proc.  Royal  Soc.'  vol.  sxiii.  1875,       anemofilo  delle  Composite,'  1871, 
p.  351. 


Chap.  X.  SEXUAL  RELATIONS   OF   PLANTS.  409 

wind.  In  the  above  two  classes  taken  together  there 
are  thirty-eight  anemophiious  and  thirty -six  ento- 
mophilous  genera ;  whereas  in  the  great  mass  of 
hermaphrodite  plants  the  proportion  of  anemophiious 
to  entomophilous  genera  is  extremely  small.  The 
cause  of  this  remarkable  difference  may  be  attributed 
to  anemophiious  plants  having  retained  in  a  greater 
degree  than  the  entomophilous  a  primordial  condi- 
tion, in  which  the  sexes  were  separated  and  their 
mutual  fertilisation  effected  by  means  of  the  wind. 
That  the  earliest  and  lowest  members  of  the  vegetable 
kingdom  had  their  sexes  separated,  as  is  still  the  case 
to  a  large  extent,  is  the  opinion  of  a  high  authority, 
Nageli.*  It  is  indeed  difficult  to  avoid  this  con- 
clusion, if  we  admit  the  view,  which  seems  highly 
probable,  that  the  conjugation  of  the  Algse  and  of 
some  of  the  simplest  animals  is  the  first  step  towards 
sexual  reproduction ;  and  if  we  further  bear  in  mind 
that  a  greater  and  greater  degree  of  differentiation 
between  the  cells  which  conjugate  can  be  traced, 
thus  leading  apparently  to  the  development  of  the 
two  sexual  forms.f  We  have  also  seen  that  as 
plants  became  more  highly  developed  and  affixed  to 
the  ground,  they  would  be  compelled  to  be  anemo- 
phiious in  order  to  intercross.  Therefore  all  plants 
which  have  not  since  been  greatly  modified,  would 
tend  still  to  be  both  diclinous  and  anemophiious ;  and 
we  can  thus  understand  the  connexion  between  these 
two   states,  although  they  appear  at  first  sight  quite 


*  '  Entstehung  und  Begriflf  der  Also,   Engelmann,    "T^eber  Ent- 

naturiiist.  Art,'  1S65.  p.  22.  wiokelung  von  Infuporien,"  'Mor- 

t  See    the    interesting  discus-  phol.    Jahrbuch,'   B.    i.   p.    573. 

tion  on  this  whole  subject  by  O.  Also,  D-.  A.  Dodel,  ''Die  Kraus- 

Biit>chii  in  his  '  Studien  iiher  die  haar-Aljje,"  '  Pringshtims  Jahrb. 

ersteiiEntwk-kelungsvorgangeder  f.  wiss.  Bot,'  B.  x. 
Eizelle,'  &c.  1876,  pp.  207-219. 


410  SEXUAL  RELATIONS  OF  PLANTS.  Chap.  X. 

disconnected.  If  this  view  is  correct,  plants  rnnst  have 
been  rendered  hermaphrodites  at  a  later  though  still 
very  early  period,  and  entomophilous  at  a  yet  later 
period,  namely,  after  the  development  of  winged  insects. 
So  that  the  relationship  between  hermaphroditism  and 
fertilisation  by  means  of  insects  is  likewise  to  a  certain 
extent  intelligible. 

Why  the  descendants  of  plants  which  were  originally 
dioecious,  and  which  therefore  profited  by  always  inter- 
crossing with  another  individual,  should  have  been 
converted  into  hermaphrodites,  may  perhaps  be  ex- 
plained by  the  risk  which  they  ran,  especially  as  long  as 
they  were  anemophilous,  of  not  being  always  fertilised, 
and  consequently  of  not  leaving  offspring.  This  latter 
evil,  the  greatest  of  all  to  any  organism,  would  have 
been  much  lessened  by  their  becoming  hermaphrodites, 
though  with  the  contingent  disadvantage  of  frequent 
self-fertilisation.  By  what  graduated  steps  an  herma- 
phrodite condition  was  acquired  we  do  not  know.  But 
we  can  see  that  if  a  lowly  organised  form,  in  which 
the  two  sexes  were  represented  by  somewhat  different 
individuals,  were  to  increase  by  budding  either  before 
or  after  conjugation,  the  two  incipient  sexes  would 
be  capable  of  appearing  by  buds  on  the  same  stock, 
as  occasionally  occurs  with  various  characters  at  the 
present  day.  The  organism  would  then  be  in  a 
monoecious  condition,  and  this  is  probably  the  first 
step  towards  hermaphroditism ;  for  if  very  simple 
male  and  female  flowers  on  the  same  stock,  each  con- 
sisting of  a  single  stamen  or  pistil,  were  brought  close 
together  and  surrounded  by  a  common  envelope,  in 
nearly  the  same  manner  as  with  the  florets  of  the 
Compositse,  we  should  have  an  hermaphrodite  flower. 

There  seems  to  be  no  limit  to  the  changes  which 
organisms  undergo  under  changing  conditions  of  life  ; 


Chap.  X.  SEXUAL   KELATIONS   OF   PLANTS.  411 

and  some  hermaphrodite  plants,  descended  as  we  must 
believe  from  aboriginally  diclinous  plants,  have  had 
their  sexes  again  separated.  That  this  has  occurred, 
we  may  infer  from  the  presence  of  rudimentary  stamens 
in  the  flowers  of  some  individuals,  and  of  rudimentary 
pistils  in  the  flowers  of  other  individuals,  for  example 
in  Lychnis  dioica.  But  a  conversion  of  this  kind  will 
not  have  occurred  unless  cross -fertilisation  was  already 
assured,  generally  by  the  agency  of  insects  ;  but  why 
the  production  of  male  and  female  flowers  on  distinct 
plants  should  have  been  advantageous  to  the  species, 
cross-fertilisation  having  been  previously  assured,  is 
far  from  obvious.  A  plant  might  indeed  produce  twice 
as  many  seeds  as  were  necessary  to  keep  up  its  numbers 
under  new  or  changed  conditions  of  life  ;  and  if  it  did 
not  vary  by  bearing  fewer  flowers,  and  did  vary  in  the 
state  of  its  reproductive  organs  (as  often  occurs  under 
cultivation),  a  wasteful  expenditure  of  seeds  and  pollen 
would  be  saved  by  the  flowers  becoming  diclinous. 

A  related  point  is  worth  notice.  I  remarked  in  my 
Origin  of  Species  that  in  Britain  a  much  larger  pro- 
portion of  trees  and  bushes  than  of  herbaceous  plants 
have  their  sexes  separated ;  and  so  it  is,  according  to 
Asa  Gray  and  Hooker,  in  North  America  and  New 
Zealand.*     It  is,  however,  doubtful  how  far  this  rule 


*  I  find  in  the  '  London  Cata-  and  Dr.  Hooker  calculates  that 
logue  of  British  Plants,'  that  there  out  of  about  75<>  phanerogamic 
are  thirty-two  indigenous  trees  plants  inhabiting  the  inlands,  no 
and  bushes  in  Great  Britain,  less  than  1-8  are  trees,  belong- 
classed  under  nine  families;  but  ing  to  thirty-five  families.  Of 
to  err  on  the  safe  side,  I  have  Ihese  108  trees,  fifty-two,  or 
counted  only  six  species  of  wil-  very  nearly  half,  h  ve  their  ^exe8 
L  iws.  Of  the  thirty-two  trees  and  mi  >re  or  less  separated.  Of  bushes 
bushes,  nineteen,  or  more  than  there  are  149,  of  which  sixty- 
half,  have  their  sexes  separated;  one  have  their  sexes  in  the  same 
and  this  is  an  enormous  propor-  state;  whilst  of  the  remaining 
tion  compared  with  other  British  5U0  herbaceous  plants  only  121, 
plants.  New  Zealand  abounds  or  less  than  a  fourth,  have  their 
with  diclinous  plants  and  trees ;  sexes    separated.      Lastly,    Profi 


412  SEXUAL  KELATIONS   OF  PLANTS.  Chap.  X. 

holds  good  generally,  and  it  certainly  does  not  do  so 
in  Australia.  But  I  have  been  assured  that  the  flowers 
of  the  prevailing  Australian  trees,  namely,  the 
Myrtaceas,  swarm  with  insects,  and  if  they  are  dicho- 
gamous  they  would  be  practically  diclinous.*  As  far 
as  anemophilous  plants  are  concerned,  we  know  that 
they  are  apt  to  have  their  sexes  separated,  and  we  can 
see  that  it  would  be  an  unfavourable  circumstance  for 
them  to  bear  their  flowers  very  close  to  the  ground,  as 
their  pollen  is  liable  to  be  blown  high  up  in  the  air ;  f 
but  as  the  culms  of  grasses  give  sufficient  elevation, 
we  cannot  thus  account  for  so  many  trees  and  bushes 
being  diclinous.  We  may  infer  from  our  previous 
discussion  that  a  tree  bearing  numerous  hermaphrodite 
flowers  would  rarely  intercross  with  another  tree, 
except  by  means  of  the  pollen  of  a  distinct  individual 
being  prepotent  over  the  plant's  own  pollen.  Now  the 
separation  of  the  sexes,  whether  the  plant  were  anemo- 
philous or  entomophilous,  would  most  effectually  bar 
self-fertilisation,  and  this  may  be  the  cause  of  so  many 
trees  and  bushes  being  diclinous.  Or  to  put  the  case 
in  another  way,  a  plant  would  be  better  fitted  for 
development  into  a  tree,  if  the  sexes  were  separated, 
than  if  it  were  hermaphrodite  ;  for  in  the  former  case 
its  numerous  flowers  would  be  less  liable  to  continued 


Asa  Gray  informs  me  that  in  the  stigma  in  the  several  genera  is 

United  States  there  are  132  native  screened  from   the  action  of  the 

trees    (belonging   to    twenty-five  pollen  from  the  same  flower.    For 

families)  of  which  ninety-five  (be-  instance,  in  Synaphea  "  the  stigma 

longing    to    seventeen    families)  is   held  by  the  eunuch  (i.e.,  one 

"Lave   their  sexes  more  or  less  of  the  stamens  which  is  barren) 

separated,    for  ihe    greater  part  safe  from  all  pollution  from  her 

decidedly  separated."  brother  anthers,  and  is  preserved 

*  With  respect  to  the  Proteacese  intact  for  any  pollen  that  maybe 

of    Australia,    Mr.    Bentham  re-  inserte  1    by    insects    and    other 

marks  ('  Journal  Linn.  Soc.  Bot.'  agencies." 

vol.  xiii.  1871,  pp.  58,  64)  on  the  t  Kerner,     '  Schutzmittel    des 

various  contrivances  by  which  the  Pollens/  1873,  p.  i. 


Chap.  X.  SEXUAL  KELATIONS   OF  PLANTS.  413 

self-fertilisation.  But  it  should  also  be  observed  that 
the  long  life  of  a  tree  or  bush  permits  of  the  separation 
of  the  sexes,  with  much  less  risk  of  evil  from  impreg- 
nation occasionally  failing  and  seeds  not  being  pro- 
duced, than  in  the  case  of  short-lived  plants.  Hence 
it  probably  is,  as  Lecoq  has  remarked,  that  annual 
plants  are  rarely  dioecious. 

Finally,  we  have  seen  reason  to  believe  that  the 
higher  plants  are  descended  from  extremely  low  forms 
which  conjugated,  and  that  the  conjugating  indi- 
viduals differed  somewhat  from  one  another, — the  one 
representing  the  male  and  the  other  the  female — so 
that  plants  were  aboriginally  dioecious.  At  a  very 
early  period  such  lowly  organised  dioecious  plants 
probably  gave  rise  by  budding  to  monoecious  plants 
with  the  two  sexes  borne  by  the  same  individual ;  and 
by  a  still  closer  union  of  the  sexes  to  hermaphrodite 
plants,  which  are  now  much  the  commonest  form.  * 
As  soon  as  plants  became  affixed  to  the  ground,  their 
pollen  must  have  been  carried  by  some  means  from 
flower  to  flower,  at  first  almost  certainly  by  the  wind, 
then  by  pollen-devouring,  and  afterwards  by  nectar- 
seeking  insects.  During  subsequent  ages  some  few 
entomophilous  plants  have  been  again  rendered  anemo- 
philous,  and  some  hermaphrodite  plants  have  had  their 
sexes  again  separated ;  and  we  can  vaguely  see  the 
advantages  of  such  recurrent  changes  under  certain 
conditions. 

Dioecious   plants,   however   fertilised,  have  a  great 

*    There     is     a     considerable  duals,  which  represented  the  two 

amount   of  evidence  that  all  the  incipient  sexes.    On  this  view,  the 

higher  animals  are  the  descend-  higher    animals    may    now    owe 

ants  of  hermaphrodites;  and  it  is  their  bilateral  structure,  with  all 

a  curious  problem  whether  such  their  organs  double  at  an  early 

hermaphroditism  may   not   have  embryouic   period,  to   the   fusion 

been  the  result  of  the  conjugation  or  conjugation  of  two  primordial 

of  two  slightly  different  indivi-  individuals. 


£14  SEXUAL  KELATTONS   OF   PLANTS.  Chap.  X. 

advantage  over  other  plants  in  their  cross-fertilisation 
being  assured.  But  this  advantage  is  gained  in  the 
case  of  anernophilous  species  at  the  expense  of  the 
production  of  an  enormous  superfluity  of  pollen,  with 
some  risk  to  them  and  to  entomophilous  species  of 
their  fertilisation  occasionally  failing.  Half  the  in- 
dividuals, moreover,  namely,  the  males,  produce  no 
seed,  and  this  might  possibly  be  a  disadvantage. 
Delpino  remarks  that  dioecious  plants  cannot  spread  so 
easily  as  monoecious  and  hermaphrodite  species,  for  a 
single  individual  which  happened  to  reach  some  new 
site  could  not  propagate  its  kind ;  but  it  may  be 
doubted  whether  this  is  a  serious  evil.  Monoecious 
plants  can  hardly  fail  to  be  to  a  large  extent  dioecious 
in  function,  owing  to  the  lightness  of  their  pollen  and 
to  the  wind  blowing  laterally,  with  the  great  addi- 
tional advantage  of  occasionally  or  often  producing 
some  self-fertilised  seeds.  When  they  are  also  di- 
chogamous,  they  are  necessarily  dioecious  in  function. 
Lastly,  hermaphrodite  plants  can  generally  produce  at 
least  some  self-fertilised  seeds,  and  they  are  at  the 
same  time  capable,  through  the  various  means  specified 
in  this  chapter,  of  cross-fertilisation.  When  their 
structure  absolutely  prevents  self-fertilisation,  they  are 
in  the  same  relative  position  to  one  another  as 
monoecious  or  dioecious  plants,  with  what  may  be  an 
advantage,  namely,  that  every  flower  is  capable  of 
yielding  seeds. 


Chap.  XL  HABITS   OF  INSECTS.  415 


CHAPTEK  XI. 

The  Habits  of  Insects  in  relation  to  the  Fertilisation  of 
Flowers. 

Insects  visit  the  flowers  of  the  same  species  as  long  as  they  can—  Cause 
of  this  habit — Means  by  whi^h  bees  recognise  the  flowers  of  the 
same  species — Sudden  secretion  of  nectar — Nectar  of  certain  flowers 
unattractive  to  certain  insects— Industry  of  bees,  and  the  number 
of  flowers  visited  within  a  short  time — Perforation  of  the  corolla 
by  bees — Skill  shown  in  the  operation — Hive-bees  profit  by  the 
holes  made  by  humble-bees — Effects  of  hahit — The  motive  for  per- 
forating flowers  to  save  time — Flowers  growing  in  crowded  masses 
chiefly  perforated. 

Bees  and  various  other  insects  must  be  directed  by 
instinct  to  search  flowers  for  nectar  and  pollen,  as 
they  act  in  this  manner  without  instruction  as  soon  as 
they  emerge  from  the  pupa  state.  Their  instincts, 
however,  are  not  of  a  specialised  nature,  for  they  visit 
many  exotic  flowers  as  readily  as  the  endemic  kinds, 
and  they  often  search  for  nectar  in  flowers  which  do 
not  secrete  any  ;  and  they  may  be  seen  attempting  to 
suck  it  out  of  nectaries  of  such  length  that  it  cannot 
be  reached  by  them.*  All  kinds  of  bees  and  certain 
other  insects  usually  visit  the  flowers  of  the  same  species 
as  long  as  they  can,  before  going  to  another  species. 
This  fact  was  observed  bv,  Aristotle  with  respect  to  the 

*  See,  on  Ibis  subject,  H.  Miil-  Hymenoptera  have  inherited  from 

ler,   '  Befi uchtmrg,'   &v.    p,   4:7;  some    early    nectar-sucking    pro- 

and    Sir    J.    Lubbock's   '  Brit  sh  genitor   greatt-r   skill  in  robbing 

Wild  Holers.'  &c.  p.  20.     Mull^r  Mowers  1han  that  which    is   dis- 

assicns  ('  Bienen   Zeitung,'  June  played   by  insects    belonging    to 

1876,  p.  119)  good  reasons  for  his  the  other  Orders, 
belief  that  bees  and  many  other 


416  HABITS   OF  INSECTS  Chap.  XL 

hive-bee  more  than  2000  years  ago,  and  was  noticed 
by  Dobbs  in  a  paper  published  in  1736  in  the  Philo- 
sophical Transactions.  It  may  be  observed  by  any 
one,  both  with  hive  and  humble-bees,  in  every  flower- 
garden;  not  that  the  habit  is  invariably  followed.  Mr, 
Bennett  watched  for  several  hours*  many  plants  of 
Lamium  album,  L.  purpureum,  and  another  Labiate 
plant,  Nepeta  glechoma,  all  growing  mingled  together 
on  a  bank  near  some  hives  ;  and  he  found  that  each 
bee  confined  its  visits  to  the  same  species.  The  pollen 
of  these  three  plants  differs  in  colour,  so  that  he  was 
able  to  test  his  observations  by  examining  that  which 
adhered  to  the  bodies  of  the  captured  bees,  and  he 
found  one  kind  on  each  bee. 

Humble  and  hive-bees  are  good  botanists,  for  they 
know  that  varieties  may  differ  widely  in  the  colour  of 
their  flowers  and  yet  belong  to  the  same  species.  I 
have  repeatedly  seen  humble-bees  flying  straight  from 
a  plant  of  the  ordinary  red  Dictamnus  fraxinella  to  a 
white  variety ;  from  one  to  another  very  differently 
coloured  variety  of  Delphinium  consolida  and  of 
Primula  veris  ;  from  a  dark  purple  to  a  bright  yellow 
variety  of  Viola  tricolor;  and  with  two  species  of 
Papaver,  from  one  variety  to  another  which  differed 
much  in  colour ;  but  in  this  latter  case  some  of  the 
bees  flew  indifferently  to  either  species,  although  pass- 
ing by  other  genera,  and  thus  acted  as  if  the  two  spe- 
cies were  merely  varieties.  H.  Miiller  also  has  seen 
hive-bees  flying  from  flower  to  flower  of  Ranunculus 
bulbosus  and  arvensis,  and  of  Trifolium  fragiferum 
and  repens;  and  even  from  blue  hyacinths  to  blue 
violets.f 

Some  species  of  Diptera  or  flies  keep  to  the  flowers 

*'  Nature,'    1S74,    June    4th,  t  'Bienen  Zeitung,' July  1876, 

p.  92.  p.  183. 


Chap.  XL    IN   RELATION   TO   CROSS-FERTILISATION.       417 

of  the  same  species  with  almost  as  much  regularity  as 
do  bees ;  aud  when  captured  they  are  found  covered 
with  pollen.  I  have  seen  Bhingia  rostrata  acting  in 
this  manner  with  the  flowers  of  Lychnis  dioica,  Ajuga 
reptans,  and  Viola  septum.  Volucella  plumosa  and  Empis 
cheiroptera  flew  straight  from  flower  to  flower  of  Myosotis 
sylvatica.  Dollchopus  nlgrlpennls  behaved  in  the  same 
manner  with  Potentllla  tormentilla  ;  and  other  Diptera 
with  JStellarla  holostea,  Hellanthemum  vulgare,  Bellis 
perennis,  Veronica  hedersefolla  and  chamaedrys  ;  but  some 
flies  visited  indifferently  the  flowers  of  these  two  latter 
species.  I  have  seen  more  than  once  a  minute  Thrips, 
with  pollen  adhering  to  its  body,  fly  from  one  flower  to 
another  of  the  same  kind ;  and  one  was  observed  by 
me  crawling  about  within  a  convolvulus  with  four 
grains  of  pollen  adhering  to  its  head,  which  were 
deposited  on  the  stigma. 

Fabricius  and  Sprengel  state  that  when  flies  have 
once  entered  the  flowers  of  Aristolochia  they  never 
escape, — a  statement  which  I  could  not  believe,  as  in 
this  case  the  insects  would  not  aid  in  the  cross-fertili- 
sation of  the  plant ;  and  this  statement  has  now  been 
shown  by  Hildebrand  to  be  erroneous,  xis  the  spathes 
of  Arum  maculatum  are  furnished  with  filaments  appa- 
rently adapted  to  prevent  the  exit  of  insects,  they 
resemble  in  this  respect  the  flowers  of  Aristolochia ;  and 
on  examining  several  spathes,  from  thirty  to  sixty 
minute  Diptera  belonging  to  three  species  were  found 
in  some  of  them  ;  and  many  of  these  insects  were  lying 
dead  at  the  bottom,  as  if  they  had  been  permanently 
entrapped.  In  order  to  discover  whether  the  living 
ones  could  escape  and  carry  pollen  to  another  plant,  I 
tied  in  the  spring  of  1842  a  fine  muslin  bag  tightly 
round  a  spathe ;  and  on  returning  in  an  hour's  time 
several  little  flies  were  crawling  about  on  the   inner 


418  HABITS  OP  INSECTS  Chap.  XL 

surface  of  the  bag.  I  then  gathered  a  spathe  and 
breathed  hard  into  it ;  several  flies  soon  crawled  out, 
and  all  without  exception  were  dusted  with  arum  pollen. 
These  flies  quickly  flew  away,  and  I  distinctly  saw 
three  of  thern  fly  to  another  plant  about  a  yard  off; 
they  alighted  on  the  inner  or  concave  surface  of  the 
spathe,  and  suddenly  flew  down  into  the  flower.  I  then 
opened  this  flower,  and  although  not  a  single  anther 
had  burst,  several  grains  of  pollen  were  lying  at  the 
bottom,  which  must  have  been  brought  from  another 
plant  by  one  of  these  flies  or  by  some  other  insect.  In 
another  flower  little  flies  were  crawling  about,  and  I 
saw  them  leave  pollen  on  the  stigmas. 

I  do  not  know  whether  Lepidoptera  generally  keep 
to  the  flowers  of  the  same  species ;  but  I  once  observed 
many  minute  moths  (I  believe  Lamjpronia  (Tinea) 
calthella)  apparently  eating  the  pollen  of  Mercurialis 
annua,  and  they  had  the  whole  front  of  their  bodies 
covered  with  pollen.  I  then  went  to  a  female  plant 
some  yards  off,  and  saw  in  the  course  of  fifteen  minutes 
three  of  these  moths  alight  on  the  stigmas.  Lepidoptera 
are  probably  often  induced  to  frequent  the  flowers  of  the 
same  species,  whenever  these  are  provided  with  a  long 
and  narrow  nectary,  as  in  this  case  other  insects  cannot 
suck  the  nectar,  which  will  thus  be  preserved  for  those 
having  an  elongated  proboscis.  No  doubt  the  Yucca 
moth*  visits  only  the  flowers  whence  its  name  is  de- 
rived, for  a  most  wonderful  instinct  guides  this  moth 
to  place  pollen  on  the  stigma,  so  that  the  ovules  may  be 
developed  on  which  the  larvae  feed.  With  respect  to 
Coleoptera,  I  have  seen  Meligethes  covered  with  pollen 
flying  from  flower  to  flower  of  the  same  species ;  and 


*  Described  by  Mr.  Eiley  in  the  '  American   Naturalist,'  voL  vii. 
Oct.  1873. 


Chap.  XL     IN   RELATION   TO   CROSS-FERTILISATION.       419 

this  must  often  occur,  as,  according  to  M.  Brisout, 
"  many  of  the  species  affect  only  one  kind  of  plant."  * 

It  must  not  be  supposed  from  these  several  statements 
that  insects  strictly  confine  their  visits  to  the  same 
species.  They  often  visit  other  species  when  only  a 
few  plants  of  the  same  kind  grow  near  together.  In  a 
flower-garden  containing  some  plants  of  CEnothera,  the 
pollen  of  which  can  easily  be  recognised,  I  found  not 
only  single  grains  but  masses  of  it  within  many  flowers 
of  Mimulus,  Digitalis,  Antirrhinum,  and  Linaria. 
Other  kinds  of  pollen  were  likewise  detected  in  these 
same  flowers.  A  large  number  of  the  stigmas  of  a  plant 
of  Thyme,  in  which  the  anthers  were  completely  aborted, 
were  examined ;  and  these  stigmas,  though  scarcely 
larger  than  a  split  needle,  were  covered  not  only  with 
pollen  of  Thyme  brought  from  other  plants  by  the  bees, 
but  with  several  other  kinds  of  pollen. 

That  insects  should  visit  the  flowers  of  the  same 
species  as  long  as  they  can,  is  of  great  importance 
to  the  plant,  as  it  favours  the  cross-fertilisation  of 
distinct  individuals  of  the  same  species ;  but  no  one 
will  suppose  that  insects  act  in  this  manner  for  the  good 
of  the  plant.  The  cause  probably  lies  in  insects  being 
thus  enabled  to  work  quicker ;  they  have  just  learnt 
how  to  stand  in  the  best  position  on  the  flower,  and  how 
far  and  in  what  direction  to  insert  their  proboscides.t 
They  act  on  the  same  principle  as  does  an  artificer 
who  has  to  make  half-a-dozen  engines,  and  who  saves 
time  by  making  consecutively  each  wheel  and  part  for 
all  of  them.  Insects,  or  at  least  bees,  seem  much  in- 
fluenced by  habit  in  all  their  manifold  operations;  and 


*  As  quotedi' i 'American  Nat.'  conclusion   with    respect   to    the 

May  1873,  p.  270.  cause   of    insects  frequenting  as 

t  Since    these    remarks    were  long  as  they  can  the  flowers  of  the 

written,  I  fi-nl  that  H.  Miiiler  has  same  species  :   '  Bienen  Zeitung,' 

some  to  alrao.-t  exactly  the  same  July  1876,  p.  182. 


420  HABITS   OF  INSECTS  Chap.  XL 

we  shall  presently  see  that  this  holds  good  in  their 
felonious  practice  of  biting  holes  through  the  corolla. 

It  is  a  curious  question  how  bees  recognise  the  flowers 
of  the  same  species.  That  the  coloured  corolla  is  the 
chief  guide  cannot  be  doubted.  On  a  fine  day,  when 
hive-bees  were  incessantly  visiting  the  little  blue  flowers 
of  Lobelia  erinus,  I  cut  off  all  the  petals  of  some,  and 
only  the  lower  striped  petals  of  others,  and  these  flowers 
were  not  once  again  sucked  by  the  bees,  although  some 
actually  crawled  over  them.  The  removal  of  the  two 
little  upper  petals  alone  made  no  difference  in  their 
visits.  Mr.  J.  Anderson  likewise  states  that  when  he  re- 
moved the  corollas  of  the  Calceolaria,  bees  never  visited 
the  flowers.*  On  the  other  hand,  in  some  large  masses  of 
Geranium  phseum  which  had  escaped  out  of  a  garden,  I 
observed  the  unusual  fact  of  the  flowers  continuing  to 
secrete  an  abundance  of  nectar  after  all  the  petals  had 
fallen  off ;  and  the  flowers  in  this  state  were  still  visited 
by  humble-bees.  But  the  bees  might  have  learnt  that 
these  flowers  with  all  their  petals  lost  were  still  worth 
visiting,  by  finding  nectar  in  those  with  only  one  or 
two  lost.  The  colour  alone  of  the  corolla  serves  as 
an  approximate  guide :  thus  I  watched  for  some  time 
humble-bees  which  were  visiting  exclusively  plants  of 


*  '  Gardeners' Chronicle,' 1853,  would  naturally  produce  seeds 
p.  534.  Kurr  cut  off  the  nectaries  under  these  circumstances ;  but  I 
from  a  large  number  of  flowers  of  am  greatly  surprised  that  Delphi- 
several  species,  and  found  that  niurn,  consalida,  as  well  as  an- 
the  greater  number  yielded  seeds ;  other  species  of  Delphinium,  and 
but  insects  probably  would  not  Viola  tricolor,  should  have  pro- 
perceive  the  loss  of  the  nectary  duced  a  fair  supply  of  seeds  when 
until  they  had  inserted  their  pro-  thus  treated;  but  it  does  not  ap- 
boscides  into  the  holes  thus  pear  that  he  compared  the  number 
formed,  and  in  doing  so  would  of  the  seed*  thus  produce  d  with 
fertilise  ihe  flowers  He  also  re-  those  yielded  by  unmutilated 
moved  the  whole  corolla  from  a  flowers  left  to  the  free  access  of 
considerable  number  of  flowers,  insects:  'Bedeutung  der  Nek- 
and  these  likewise  yielded  seeds.  tarien,'  1S33,  pp.  123-135. 
Flowers    which    are    self- fertile 


Uhap.  XI.     IN   RELATION   TO   CROSS-FERTILISATION.       421 

the  white-flowered  Spiranthes  autumnalis,  growing  on 
short  turf  at  a  considerable  distance  apart ;  and  these 
bees  often  flew  within  a  few  inches  of  several  other 
plants  with  white  flowers,  and  then  without  further  ex- 
amination passed  onwards  in  search  of  the  Spiranthes. 
Again,  many  hive-bees  which  confined  their  visits  to  the 
common  ling  {Calluna  vulgaris),  repeatedly  flew  towards 
Erica  tetralix,  evidently  attracted  by  the  nearly  similar 
tint  of  their  flowers,  and  then  instantly  passed  on  in 
search  of  the  Calluna. 

That  the  colour  of  the  flower  is  not  the  sole  guide,  is 
clearly  shown  by  the  six  cases  above  given  of  bees 
which  repeatedly  passed  in  a  direct  line  from  one 
variety  to  another  of  the  same  species,  although  they 
bore  very  differently  coloured  flowers.  I  observed  also 
bees  flying  in  a  straight  line  from  one  clump  of  a  yellow- 
flowered  CEnothera  to  every  other  clump  of  the  same 
plant  in  the  garden,  without  turning  an  inch  from 
their  course  to  plants  of  Eschscholtzia  and  others  with 
yellow  flowers  which  lay  only  a  foot  or  two  on  either 
side.  In  these  cases  the  bees  knew  the  position  of  each 
plant  in  the  garden  perfectly  well,  as  we  may  infer  by 
the  directness  of  their  flight ;  so  that  they  were  guided 
by  experience  and  memory.  But  how  did  they  discover 
at  first  that  the  above  varieties  with  differently  coloured 
flowers  belonged  to  the  same  species  ?  Improbable  as 
it  may  appear,  they  seem,  at  least  sometimes,  to*recog- 
nise  plants  even  from  a  distance  by  their  general 
aspect,  in  the  same  manner  as  we  should  do.  On  three 
occasions  I  observed  humble-bees  flying  in  a  perfectly 
straight  line  from  a  tall  larkspur  (Delphinium)  which 
was  in  full  flower  to  another  plant  of  the  same  species 
at  the  distance  of  fifteen  yards  which  had  not  as  yet  a 
single  flower  open,  and  on  which  the  buds  showed  only 
a  faint  tinge  of  blue.     Here  neither  odour  nor  the 


422  HABITS   OF   INSECTS  Ciiap.  XL 

memory  of  former  visits  could  have  come  into  play, 
and  the  tinge  of  blue  was  so  faint  that  it  could  hardly 
have  served  as  a  guide.* 

The  conspicuousness  of  the  corolla  does  not  suffice 
to  induce  repeated  visits  from  insects,  unless  nectar  is 
at  the  same  time  secreted,  together  perhaps  with 
some  odour  emitted.  I  watched  for  a  fortnight  many 
times  daily  a  wall  covered  with  Linaria  cymhalaria 
in  full  flower,  and  never  saw  a  bee  even  looking  at 
one.  There  was  then  a  very  hot  day,  and  suddenly 
many  bees  were  industriously  at  work  on  the  flowers. 
It  appears  that  a  certain  degree  of  heat  is  necessary  for 
the  secretion  of  nectar;  for  I  observed  with  Lobelia 
erinus  that  if  the  sun  ceased  to  shine  for  only  half  an 
hour,  the  visits  of  the  bees  slackened  and  soon  ceased. 
An  analogous  fact  with  respect  to  the  sweet  excretion 
from  the  stipules  of  Vieia  sativa  has  been  already 
given.  As  in  the  case  of  the  Linaria,  so  with  Pedicu- 
laris  sylvatica,  Polygala  vulgaris,  Viola  tricolor,  and  some 
species  of  Trifolium,  I  have  watched  the  flowers  day 
after  day  without  seeing  a  bee  at  work,  and  then  sud- 
denly all  the  flowers  were  visited  by  many  bees.  Now 
how  did  so  many  bees  discover  at  once  that  the  flowers 
were  secreting  nectar  ?  I  presume  that  it  must  have  been 
by  their  odour :  and  that  as  soon  as  a  few  bees  began 
to  suck  the  flowers,  others  of  the  same  and  of  different 
kinds  observed  the  fact  and  profited  by  it.  We  shall 
presently  see,  when  we  treat  of  the  perforation  of  the 
corolla,  that  bees  are  fully  capable  of  profiting  by  the 


*   A.    fact    mentioned    by    H  flowers  of  the  long-styled  form,  in 

Miiller  ('Die  Iiofruehtung,*   &c ,  which  the  anther»  are  seated  low 

p.  347)  shows  that  bees   possess  down  in  the  tubular  corolla.     Yet 

acuie  powers  of  visi  n  and  dis-  the  difference  in  aspect  between 

crimination;  for  those  engaged  in  the  long-styled  and   short-styled 

cwllecting    pollen   from    Frimula  forms  is  extremely  slight. 
elatior   invariably  passed  by  the 


Chap.  XI.     IN  EELATION   TO   CKOSS-FERTILISATION.       423 

labour  of  other  species.  Memory  also  comes  into  play, 
for,  as  already  remarked,  bees  know  the  position  of 
each  clump  of  flowers  in  a  garden.  I  have  repeatedly 
seen  them  passing  round  a  corner,  but  otherwise  in  as 
straight  a  line  as  possible,  from  one  plant  of  Fraxinella 
and  of  Linaria  to  another  and  distant  one  of  the  same 
species ;  although,  owing  to  the  intervention  of  other 
plants,  the  two  were  not  in  sight  of  each  other. 

It  would  appear  that  either  the  taste  or  the  odour  of 
the  nectar  of  certain  flowers  is  unattractive  to  hive  or  to 
humble-bees,  or  to  both ;  for  there  seems  no  other  reason 
why  certain  open  flowers  which  secrete  nectar  are  not 
visited  by  them.  The  small  quantity  of  nectar  secreted 
by  some  of  these  flowers  can  hardly  be  the  cause  of 
their  neglect,  as  hive-bees  search  eagerly  for  the  minute 
drops  on  the  glands  on  the  leaves  of  the  Prunus  lauro- 
cerasus.  Even  the  bees  from  different  hives  sometimes 
visit  different  kinds  of  flowers,  as  is  said  to  be  the  case 
by  Mr.  Grant  with  respect  to  the  Polyanthus  and  Viola 
tricolor*  I  have  known  humble-bees  to  visit  the  flowers 
of  Lobelia  fulgens  in  one  garden  and  not  in  another  at 
the  distance  of  only  a  few  miles.  The  cupful  of  nectar 
in  the  labellum  of  Epijpactis  latifolia  is  never  touched 
by  hive-  or  humble-bees,  although  I  have  seen  them 
flying  close  by ;  and  yet  the  nectar  has  a  pleasant 
taste  to  us,  and  is  habitually  consumed  by  the  common 
wasp.  As  far  as  I  have  seen,  wasps  seek  for  nectar  in 
this  country  only  from  the  flowers  of  this  Epipactis, 
Scrophularia  aquatica,  Symphoricarpus  racemosa,\  and 
Tritoma ;  the  two  former  plants  being  endemic,  and 
the  two  latter  exotic.     As  wasps  are  so  fond  of  sugar 


*  '  Gard.  Chron.'  1844,  p.  374.        three  plants  are  alone  visited  by 
f  The    same    fact    apparently      wasps  :     '  Nettarii    Estranuziali, 

holds  good  in  Italy,  for  Delpino      Bullettino  Eutomologico,'  anno  vi. 

says   that   the  flowers    of   these 
19 


424  HABITS  OF  INSECTS  Chap.  XL 

and  of  any  sweet  fluid,  and  as  they  do  not  disdain  the 
minute  drops  on  the  glands  of  Primus  laurocerasus,  it 
is  a  strange  fact  that  they  do  not  suck  the  nectar  of 
many  open  flowers,  which  they  could  do  without  the 
aid  of  a  proboscis.  Hive-bees  visit  the  flowers  of 
the  Symphoricarpus  and  Tritoma,  and  this  makes  it  all 
the  stranger  that  they  do  not  visit  the  flowers  of 
the  Epipactis,  or,  as  far  as  I  have  seen,  those  of  the 
Scrophularia  aquatica ;  although  they  do  visit  the 
flowers  of  Scrophularia  nodosa,  at  least  in  North 
America.* 

The  extraordinary  industry  of  bees  and  the  number 
of  flowers  which  they  visit  within  a  short  time,  so  that 
each  flower  is  visited  repeatedly,  must  greatly  increase 
the  chance  of  each  receiving  pollen  from  a  distinct 
plant.  When  the  nectar  is  in  any  way  hidden,  bees 
cannot  tell  without  inserting  their  proboscides  whether 
it  has  lately  been  exhausted  by  other  bees,  and 
this,  as  remarked  in  a  former  chapter,  forces  them  to 
visit  many  more  flowers  than  they  otherwise  would. 
But  they  endeavour  to  lose  as  little  time  as  they  can; 
thus  in  flowers  having  several  nectaries,  if  they  find 
one  dry  they  do  not  try  the  others,  but  as  I  have  often 
observed,  pass  on  to  another  flower.  They  work  so  in- 
dustriously and  effectually,  that  even  in  the  case  of 
social  plants,  of  which  hundreds  of  thousands  grow 
together,  as  with  the  several  kinds  of  heath,  every 
single  flower  is  visited,  of  which  evidence  will  presently 
be  given.  They  lose  no  time  and  fly  very  quickly 
from  plant  to  plant,  but  I  do  not  know  the  rate  at 
which  hive-bees  fly.  Humble-bees  fly  at  the  rate  of 
ten  miles  an  hour,  as  I  was  able  to  ascertain  in  the  case 
of  the   males   from  their  curious  habit  of  calling  at 


Silliniati's  American  Journal  of  Science,'  Aug.  1871. 


Chap.  XI.    IN   KELATION   TO   CKOSS-FEKTILISATION.       425 

certain  fixed  points,  which  made  it  easy  to  measure  the 
time  taken  in  passing  from  one  place  to  another. 

With  respect  to  the  number  of  flowers  which  bees 
visit  in  a  given  time,  I  observed  that  in  exactly  one 
minute  a  humble-bee  visited  twenty-four  of  the  closed 
flowers  of  the  Linaria  cymbalaria  ;  another  bee  visited 
in  the  same  time  twenty-two  flowers  of  the  Symphori- 
carpus  racemosa  ;  and  another  seventeen  flowers  on  two 
plants  of  a  Delphinium.  In  the  course  of  fifteen 
minutes  a  single  flower  on  the  summit  of  a  plant  of 
CEnothera  was  visited  eight  times  by  several  humble- 
bees,  and  I  followed  the  last  of  these  bees,  whilst 
it  visited  in  the  course  of  a  few  additional  minutes 
every  plant  of  the  same  species  in  a  large  flower- 
garden.  In  nineteen  minutes  every  flower  on  a  small 
plant  of  Nemophila  insignis  was  visited  twice.  In  one 
minute  six  flowers  of  a  Campanula  were  entered  by 
a  pollen-collecting  hive-bee ;  and  bees  when  thus 
employed  work  slower  than  when  sucking  nectar. 
Lastly,  seven  flower-stalks  on  a  plant  of  Dictamnus 
fraxinella  were  observed  on  the  15th  of  June  1841  during 
ten  minutes ;  they  were  visited  by  thirteen  humble-bees 
each  of  which  entered  many  flowers.  On  the  22nd  the 
same  flower-stalks  were  visited  within  the  same  time  by 
eleven  humble-bees.  This  plant  bore  altogether  280 
flowers,  and  from  the  above  data,  taking  into  con- 
sideration how  late  in  the  evening  humble-bees  work, 
each  flower  must  have  been  visited  at  least  thirty  times 
daily,  and  the  same  flower  keeps  open  during  several 
days.  The  frequency  of  the  visits  of  bees  is  also  some- 
times shown  by  the  manner  in  which  the  petals  are 
scratched  by  their  hooked  tarsi ;  I  have  seen  large  beds 
of  Mimulus,  Stachys,  and  Lathyrus  with  the  beauty 
of  their  flowers  thus  sadly  defaced. 

Perforation  of  the  Corolla  by  Bees. — I  have  already 


£26  HABITS  OF  INSECTS.  Chap.  XI. 

alluded  to  bees  biting  boles  in  flowers  for  the  sake  of 
obtaining  the  nectar.  They  often  act  in  this  manner, 
both  with  endemic  and  exotic  species,  in  many  parts  of 
Europe,  in  the  United  States,  and  in  the  Himalaya ; 
and  therefore  probably  in  all  parts  of  the  world.  The 
plants,  the  fertilisation  of  which  actually  depends  on 
insects  entering  the  flowers,  will  fail  to  produce  seed 
when  their  nectar  is  stolen  from  the  outside ;  and  even 
with  those  species  which  are  capable  of  fertilising 
themselves  without  any  aid,  there  can  be  no  cross- 
fertilisation,  and  this,  as  we  know,  is  a  serious  evil 
in  most  cases.  The  extent  to  which  humble-bees 
carry  on  the  practice  of  biting  holes  is  surprising :  a 
remarkable  case  was  observed  by  me  near  Bourne- 
mouth, where  there  were  formerly  extensive  heaths. 
I  took  a  long  walk,  and  every  now  and  then  gathered 
a  twig  of  Erica  tetralix,  and  when  I  had  got  a  handful 
all  the  flowers  were  examined  through  a  lens.  This 
process  was  repeated  many  times ;  but  though  many 
hundreds  were  examined,  I  did  not  succeed  in  finding 
a  single  flower  which  had  not  been  perforated. 
Humble-bees  were  at  the  time  sucking  the  flowers 
through  these  perforations.  On  the  following  day  a 
large  number  of  flowers  were  examined  on  another 
heath  with  the  same  result,  but  here  hive-bees  were 
sucking  through  the  holes.  This  case  is  all  the 
more  remarkable,  as  the  innumerable  holes  had  been 
made  within  a  fortnight,  for  before  that  time  I  saw  the 
bees  everywhere  sucking  in  the  proper  manner  at  the 
mouths  of  the  corolla.  In  an  extensive  flower-garden 
some  large  beds  of  Salvia  grahami,  Stachys  coccinea, 
and  Pentstemon  argutus  (?)  had  every  flower  per- 
forated, and  many  scores  were  examined.  I  have  seen 
whole  fields  of  red  clover  (Trifolium  pratense)  in  the 
Bame  state.     Dr.  Ogle  found  that  90  per  cent,  of  the 


Chap.  XL         PERFORATION   OF   THE   COROLLA.  427 

flowers  of  Salvia  glutinosa  had  been  bitten.  In  the 
United  States  Mr.  Bailey  says  it  is  difficult  to  find  a 
blossom  of  the  native  Gerardia  yedicvlaria  without  a 
hole  in  it ;  and  Mr.  Gentry,  in  speaking  of  the  intro- 
duced Wistaria  sinensis,  says  "  tha,t  nearly  every  flower 
had  been  perforated."  * 

As  far  as  I  have  seen,  it  is  always  humble-bees  which 
first  bite  the  holes,  and  they  are  well  fitted  for  the  work 
by  possessing  powerful  mandibles ;  but  hive-bees  after- 
wards profit  by  the  holes  thus  made.  Dr.  H.  Miiller, 
however,  writes  to  me  that  hive-bees  sometimes  bite 
holes  through  the  flowers  of  Erica  tetralix.  No  insects 
except  bees,  with  the  single  exception  of  wasps  in  the 
case  of  Tritoma,  have  sense  enough,  as  far  as  I  have 
observed,  to  profit  by  the  holes  already  made.  Even 
humble-bees  do  not  always  discover  that  it  would  be 
advantageous  to  them  to  perforate  certain  flowers. 
There  is  an  abundant  supply  of  nectar  in  the  nectary 
of  Tropeeolum  tricolor,  yet  I  have  found  this  plant 
untouched  in  more  than  one  garden,  while  the  flowers 
of  other  plants  had  been  extensively  perforated ;  but 
a  few  years  ago  Sir  J.  Lubbock's  gardener  assured 
me  that  he  had  seen  humble-bees  boring  through 
the  nectary  of  this  Tropaeolum.  Muller  has  observed 
humble-bees  trying  to  suck  at  the  mouths  of  the 
flowers  of  Primula  elatior  and  of  an  Aquilegia,  and, 
failing  in  their  attempts,  they  made  holes  through 
the  corolla ;  but  they  often  bite  holes,  although  they 
could  with  very  little  more  trouble  obtain  the 
nectar  in  a  legitimate  manner  by  the  mouth  of  the 
corolla. 

Dr.  W.  Ogle  has  communicated  to  me  a  curious  case. 

*  Dr.  Ogle,  'Pop.  Science  Re-      p.  690.     Gentry,  ibid.  May  1875, 
view,'  July  1869,  p.  267.     Bailey,       p.  264. 
American  Naturalist,'  Nov.  1873, 


428  HABITS  OP  INSECTS.  Chap.  XL 

He  gathered  in  Switzerland  100  flower-sterns  of  the 
common  blue  variety  of  the  monkshood  (Aconitum 
napellus),  and  not  a  single  flower  was  perforated;  he 
then  gathered  100  stems  of  a  white  variety  growing 
close  by,  and  every  one  of  the  oj)en  flowers  had  been 
perforated.  This  surprising  difference  in  the  state  of 
the  flowers  may  be  attributed  with  much  probability 
to  the  blue  variety  being  distasteful  to  bees,  from  the 
presence  of  the  acrid  matter  which  is  so  general  in  the 
Ranunculaceae,  and  to  its  absence  in  the  white  variety 
in  correlation  with  the  loss  of  the  blue  tint.  Accord- 
ing to  Sprengel,*  this  plant  is  strongly  proterandrous  ; 
it  would  therefore  be  more  or  less  sterile  unless  bees 
carried  pollen  from  the  younger  to  the  older  flowers. 
Consequently  the  white  variety,  the  flowers  of  which 
were  always  bitten  instead  of  being  properly  entered 
by  the  bees,  would  fail  to  yield  the  full  number 
of  seeds  and  would  be  a  comparatively  rare  plant, 
as  Dr.  Ogle  informs  me  was  the  case. 

Bees  show  much  skill  in  their  manner  of  working, 
for  they  always  make  their  holes  from  the  outside 
close  to  the  spot  where  the  nectar  lies  hidden  within 
the  corolla.  All  the  flowers  in  a  large  bed  of  Stachys 
coccinea  had  either  one  or  two  slits  made  on  the  upper 
side  of  the  corolla  near  the  base.  The  flowers  of  a 
Mirabilis  and  of  Salvia  coccinea  were  perforated  in  the 
same  manner  ;  whilst  those  of  Salvia  grahami,  in  which 
the  calyx  is  much  elongated,  had  both  the  calyx  and  the 
corolla  invariably  perforated.  The  flowers  of  Pentstemon 
argutus  are  broader  than  those  of  the  plants  just  named, 
and  two  holes  alongside  each  other  had  here  always 
been  made  just  above  the  calyx.  In  these  several  cases 
the  perforations  were  on  the  upper  side,  but  in  Antir- 


*  'Das  Entdeckte,'  &c.  p.  278. 


Chap.  XL    PEKFOEATTON  OF  THE  COBOLLA.       429 

rliinum  majus  one  or  two  holes  had  been  made  on  the 
lower  side,  close  to  the  little  protuberance  which  re- 
presents the  nectary,  and  therefore  directly  in  front  of 
and  close  to  the  spot  where  the  nectar  is  secreted. 

But  the  most  remarkable  case  of  skill  and  judgment 
known  to  me,  is  that  of  the  perforation  of  the  flowers  of 
Lathyrus  sylvestris,  as  described  by  my  son  Francis.* 
The  nectar  in  this  plant  is  enclosed  within  a  tube, 
formed  by  the  united  stamens,  which  surround  the 
pistil  so  closely  that  a  bee  is  forced  to  insert  its 
proboscis  outside  the  tube ;  but  two  natural  rounded 
passages  or  orifices  are  left  in  the  tube  near  the  base, 
in  order  that  the  nectar  may  be  reached  by  the  bees. 
Now  my  son  found  in  sixteen  out  of  twenty-four  flowers 
on  this  plant,  and  in  eleven  out  of  sixteen  of  those  on 
the  cultivated  everlasting  pea,  which  is  either  a  variety 
of  the  same  species  or  a  closely  allied  one,  that  the 
left  passage  was  larger  than  the  right  one.  And  here 
comes  the  remarkable  point, — the  humble-bees  bite  holes 
through  the  standard-petal,  and  they  always  operated 
on  the  left  side  over  the  passage,  which  is  generally 
the  larger  of  the  two.  My  son  remarks  :  "  It  is  difficult 
to  say  how  the  bees  could  have  acquired  this  habit. 
Whether  they  discovered  the  inequality  in  the  size  of 
the  nectar-holes  in  sucking  the  flowers  in  the  proper 
way,  and  then  utilised  this  knowledge  in  determining 
where  to  gnaw  the  hole ;  or  whether  they  found  out 
the  best  situation  by  biting  through  the  standard  at 
various  points,  and  afterwards  remembered  its  situation 
in  visiting  other  flowers.  But  in  either  case  they  show  a 
remarkable  power  of  making  use  of  what  they  have 
learnt  by  experience."  It  seems  probable  that  bees 
owe  their  skill  in  biting  holes  through  flowers  of  all 


1 Nature,'  Jan.  8, 1874,  p.  189. 


430  HABITS   OF  INSECTS.  Chap.  XL 

kinds  to  their  having  long  practised  the  instinct  of 
moulding  cells  and  pots  of  wax,  or  of  enlarging  their 
old  cocoons  with  tubes  of  wax ;  for  they  are  thus 
compelled  to  work  on  the  inside  and  outside  of  the 
same  object. 

In  the  early  part  of  the  summer  of  1857  I  was 
led  to  observe  during  some  weeks  several  rows  of  tho 
scarlet  kidney-bean  (Phaseolus  multiflorus),  whilst 
attending  to  the  fertilisation  of  this  plant,  and  daily 
saw  humble-  and  hive-bees  sucking  at  the  mouths 
of  the  flowers.  But  one  day  I  found  several  humble- 
bees  employed  in  cutting  holes  in  flower  after  flower ; 
and  on  the  next  day  every  single  hive-bee,  without 
exception,  instead  of  alighting  on  the  left  wing-petal 
and  sucking  the  flower  in  the  proper  manner,  flew 
straight  without  the  least  hesitation  to  the  calyx,  and 
sucked  through  the  holes  which  had  been  made  only 
the  day  before  by  the  humble-bees;  and  they  con- 
tinued this  habit  for  many  following  days.*  Mr.  Belt 
has  communicated  to  me  (July  28th,  1874)  a  similar 
case,  with  the  sole  difference  that  less  than  half  of  the 
flowers  had  been  perforated  by  the  humble-bees; 
nevertheless,  all  the  hive-bees  gave  up  sucking  at  the 
mouths  of  the  flowers  and  visited  exclusively  the  bitten 
ones.  Now  how  did  the  hive-bees  find  out  so  quickly 
that  holes  had  been  made  ?  Instinct  seems  to  be  out 
of  the  question,  as  the  plant  is  an  exotic.  The  holes 
cannot  be  seen  by  bees  whilst  standing  on  the  wing- 
petals,  where  they  had  always  previously  alighted. 
From  the  ease  with  which  bees  were  deceived  when  the 
petals  of  Lobelia  erinus  were  cut  off,  it  was  clear  that 
in  this  case  they  were  not  guided  to  the  nectar  by  its 
smell;   and  it  may  be  doubted  whether  they  were 


*  « Gard.  Chron.*  1857,  p.  725. 


Chap.  XI.        PERFORATION   OF   THE   COROLLA.  431 

attracted  to  the  holes  in  the  flowers  of  the  Phaseolus 
by  the  odour  emitted  from  them.  Did  they  perceive 
the  holes  by  the  sense  of  touch  in  their  proboscides, 
whilst  sucking  the  flowers  in  the  proper  manner,  and 
then  reason  that  it  would  save  them  time  to  alight  on 
the  outside  of  the  flowers  and  use  the  holes?  This 
seems  almost  too  abstruse  an  act  of  reason  for  bees ; 
and  it  is  more  probable  that  they  saw  the  humble-bees 
at  work,  and  understanding  what  they  were  about, 
imitated  them  and  took  advantage  of  the  shorter  path 
to  the  nectar.  Even  with  animals  high  in  the  scale, 
such  as  monkeys,  we  should  be  surprised  at  hearing 
that  all  the  individuals  of  one  species  within  the 
space  of  twenty-four  hours  understood  an  act  per- 
formed by  a  distinct  species,  and  profited  by  it. 

I  have  repeatedly  observed  with  various  kinds 
of  flowers  that  all  the  hive  and  humble-bees  which 
were  sucking  through  the  perforations,  flew  to  them, 
whether  on  the  upper  or  under  side  of  the  corolla, 
without  the  least  hesitation;  and  this  shows  how 
quickly  all  the  individuals  within  the  district  had 
acquired  the  same  knowledge.  Yet  habit  comes  into 
play  to  a  certain  extent,  as  in  so  many  of  the  other 
operations  of  bees.  Dr.  Ogle,  Messrs.  Farrer  and 
Belt  have  observed  in  the  case  of  Phaseolus  multijlorus* 
that  certain  individuals  went  exclusively  to  the  per- 
forations, while  others  of  the  same  species  visited 
only  the  mouths  of  the  flowers.  I  noticed  in  1861 
exactly  the  same  fact  with  Trifolium  pratense.  So  per- 
sistent is  the  force  of  habit,  that  when  a  bee  which  is 
visiting  perforated  flowers  comes  to  one  which  has  not 
been  bitten,  it  does  not  go  to  the  mouth,  but  instantly 

*  Dr.  Ogle,  'Pop.  Science  Re-       Hist.'  4th  series,  vol.  ii.  1868,  p. 
•view,'  April   1870,   p.    167.    Mr.       258.  Mr.  Belt  in  a  letter  to  me. 
Fairer, '  Annals  and  Mag.  of  Nat. 


432  HABITS   OF  INSECTS.  Chap.  XL 

flies  away  in  search  of  another  bitten  flower.  Never- 
theless, I  once  saw  a  humble-bee  visiting  the  hybrid 
Rhododendron  azaloides,  and  it  entered  the  mouths 
of  some  flowers  and  cut  holes  into  the  others.  Dr. 
H.  Miiller  informs  me  that  in  the  same  district  he  has 
seen  some  individuals  of  Bomhus  mastnicatus  boring 
through  the  calyx  and  corolla  of  Rhinanthus  alectero- 
lophus,  and  others  through  the  corolla  alone.  Different 
species  of  bees  may,  however,  sometimes  be  observed 
acting  differently  at  the  same  time  on  the  same  plant. 
I  have  seen  hive-bees  sucking  at  the  mouths  of  the 
flowers  of  the  common  bean ;  humble-bees  of  one  kind 
sucking  through  holes  bitten  in  the  calyx,  and  humble- 
bees  of  another  kind  sucking  the  little  drops  of  fluid 
excreted  by  the  stipules.  Mr.  Beal  of  Michigan 
informs  me  that  the  flowers  of  the  Missouri  currant 
(Ribes  aureum)  abound  with  nectar,  so  that  children 
often  suck  them ;  and  he  saw  hive-bees  sucking 
through  holes  made  by  a  bird,  the  oriole,  and  at  the 
same  time  humble-bees  sucking  in  the  proper  manner 
at  the  mouths  of  the  flowers.*  This  statement  about 
the  oriole  calls  to  mind  what  I  have  before  said  of 
certain  species  of  humming- birds  boring  holes  through 
the  flowers  of  the  Brugmansia,  whilst  other  species 
entered  by  the  mouth. 

The  motive  which  impels  bees  to  gnaw  holes  through 
the  corolla  seems  to  be  the  saving  of  time,  for  they 
lose  much  time  in  climbing  into  and  out  of  large 
flowers,  and  in  forcing  their  heads  into  closed  ones. 
They  were  able  to  visit  nearly  twice  as  many  flowers, 
as  far  as  I  could  judge,  of  a  Stachys  and  Pentstemon 


*  The  flowers  of  the  Ribes  are  through    and  rob   seven  flowers 

however  sometimes  perforated  by  of    their    honey    in   a     minute: 

humble-bees,  and  Mr.  Bundy  says  '  American  Naturalist,'   1876,  ]> 

that    they    were    able    to    bite  238. 


Chap.  XL        PERFORATION   OP   THE   COROLLA.  433 

by  alighting  on  the  upper  surface  of  the  corolla 
and  sucking  through  the  cut  holes,  than  by  entering  in 
the  proper  way.  Nevertheless  each  bee  before  it 
has  had  much  practice,  must  lose  some  time  in 
making  each  new  perforation,  especially  when  the  per- 
foration has  to  be  made  through  both  calyx  and 
corolla.  This  action  therefore  implies  foresight,  of 
which  faculty  we  have  abundant  evidence  in  their 
building  operations ;  and  may  we  not  further  believe 
that  some  trace  of  their  social  instinct,  that  is,  of 
working  for  the  good  of  other  members  of  the  com- 
munity, may  here  likewise  play  a  part  ? 

Many  years  ago  I  was  struck  with  the  fact  that 
humble-bees  as  a  general  rule  perforate  flowers  only 
when  these  grow  in  large  numbers  near  together.  In 
a  garden  where  there  were  some  very  large  beds  of 
Stachys  coecinea  and  of  Pentstemon  argutus,  every  single 
flower  was  perforated,  but  I  found  two  plants  of  the 
former  species  growing  quite  separate  with  their  petals 
much  scratched,  showing  that  they  had  been  frequently 
visited  by  bees,  and  yet  not  a  single  flower  was 
perforated.  I  found  also  a  separate  plant  of  the 
Pentstemon,  and  saw  bees  entering  the  mouth  of  the 
corolla,  and  not  a  single  flower  had  been  perforated.  In 
the  following  year  (1842)  I  visited  the  same  garden 
several  times :  on  the  19th  of  July  humble-bees  were 
sucking  the  flowers  of  Stachys  coecinea,  and  Salvia 
grahami  in  the  proper  manner,  and  none  of  the  corollas 
were  perforated.  On  the  7th  of  August  all  the  flowers 
were  perforated,  even  those  on  some  few  plants  of  the 
Salvia  which  grew  at  a  little  distance  from  the  great 
bed.  On  the  21st  of  August  only  a  few  flowers  on  the 
summits  of  the  spikes  of  both  species  remained  fresh, 
and  not  one  of  these  was  now  bored.  Again,  in  my  own 
garden  every  plant  in  several  rows  of  the  common  bean 


434  HABITS  OF  INSECTS.  Chap.  XI. 

had  many  flowers  perforated ;  but  I  found  three  plants 
in  separate  parts  of  the  garden  which  had  sprung  up 
accidentally,  and  these  had  not  a  single  flower  per- 
forated. General  Strachey  formerly  saw  many  per- 
forated flowers  in  a  garden  in  the  Himalaya,  and  he 
wrote  to  the  owner  to  inquire  whether  this  relation 
between  the  plants  growing  crowded  and  their  per- 
foration by  the  bees  there  held  good,  and  was  answered 
in  the  affirmative.  Hence  it  follows  that  the  red 
clover  (Trifolium  pratense)  and  the  common  bean  when 
cultivated  in  great  masses  in  fields, — that  Erica  tetralix 
growing  in  large  numbers  on  heaths, — rows  of  the 
scarlet  kidney-bean  in  the  kitchen-garden, — and  masses 
of  any  species  in  the  flower-garden, — are  all  eminently 
liable  to  be  perforated. 

The  explanation  of  this  fact  is  not  difficult.  Flowers 
growing  in  large  numbers  afford  a  rich  booty  to  the 
bees,  and  are  conspicuous  from  a  distance.  They  are 
consequently  visited  by  crowds  of  these  insects,  and  I 
once  counted  between  twenty  and  thirty  bees  flying 
about  a  bed  of  Pentstemon.  They  are  thus  stimulated 
to  work  quickly  by  rivalry,  and,  what  is  much  more 
important,  they  find  a  large  proportion  of  the  flowers, 
as  suggested  by  my  son,*  with  their  nectaries  sucked 
dry.  They  thus  waste  much  time  in  searching  many 
empty  flowers,  and  are  led  to  bite  the  holes,  so  as 
to  find  out  as  quickly  as  possible  whether  there  is  any 
nectar  present,  and  if  so,  to  obtain  it. 

Flowers  which  are  partially  or  wholly  sterile  unless 
visited  by  insects  in  the  proper  manner,  such  as 
those  of  most  species  of  Salvia,  of  Trifolium  pratense, 
Phaseolus  multiflorus,  &c,  will  fail  more  or  less  com- 
pletely to  produce  seeds  if  the  bees  confine  their  visits 


1  Nature,'  Jan.  8,  1874,  p.  189. 


Chap.  XI.         PERFORATION   OF   THE   COROLLA.  435 

to  the  perforations.  The  perforated  flowers  of  those 
species,  which  are  capable  of  fertilising  themselves,  will 
yield  only  self-fertilised  seeds,  and  the  seedlings  will 
in  consequence  be  less  vigorous.  Therefore  all  plants 
must  sutler  in  some  degree  when  bees  obtain  their  nectar 
in  a  felonious  manner  by  biting  holes  through  the 
corolla ;  and  many  species,  it  might  be  thought,  would 
thus  be  exterminated.  But  here,  as  is  so  general 
throughout  nature,  there  is  a  tendency  towards  a  restored 
equilibrium.  If  a  plant  suffers  from  being  perforated, 
fewer  individuals  will  be  reared,  and  if  its  nectar  is 
highly  important  to  the  bees,  these  in  their  turn  will 
suffer  and  decrease  in  number  ;  but,  what  is  much  more 
effective,  as  soon  as  the  plant  becomes  somewhat 
rare  so  as  not  to  grow  in  crowded  masses,  the  bees 
will  no  longer  be  stimulated  to  gnaw  holes  in  the 
flowers,  but  will  enter  them  in  a  legitimate  manner. 
More  seed  will  then  be  produced,  and  the  seedlings 
being  the  product  of  cross-fertilisation  will  be  vigorous, 
so  that  the  species  will  tend  to  increase  in  number,  to 
be  again  checked,  as  soon  as  the  plant  again  grows  in 
crowded  masses. 


436  GENERAL  RESULTS.  Chap.  XII. 


CHAPTER  XII. 

General  Results. 

Cross-fertilisation  proved  to  be  beneficial,  and  self-fertilisation  in- 
jurious— Allied  species  differ  greatly  in  the  means  by  which  cross- 
fertilisation  is  favoured  and  self-fertilisation  avoided — The  benefits 
and  evils  of  the  two  processes  depend  on  the  degree  of  differentiation 
in  the  sexual  elements — The  evil  effects  not  due  to  the  combination  of 
morbid  tendencies  in  the  parents — Nature  of  the  conditions  to  which 
plants  are  subjected  when  growing  near  together  in  a  state  of  nature 
or  under  culture,  and  the  effects  of  such  conditions — Theoretical 
considerations  with  respect  to  the  interaction  of  differentiated  sexual 
elements — Practical  lessons— Genesis  of  the  two  sexes — Close  corre- 
spondence between  the  effects  of  cross-fertilisation  and  self-fertilisa- 
tion, and  of  the  legitimate  and  illegitimate  unions  of  heterostyled 
plants,  in  comparison  with  hybrid  unions. 

The  first  and  most  important  of  the  conclusions  which 
may  be  drawn  from  the  observations  given  in  this 
volume,  is  that  cross-fertilisation  is  generally  beneficial, 
and  self-fertilisation  injurious.  This  is  shown  by  the 
difference  in  height,  weight,  constitutional  vigour,  and 
fertility  of  the  offspring  from  crossed  and  self-fertilised 
flowers,  and  in  the  number  of  seeds  produced  by  the 
parent-plants.  With  respect  to  the  second  of  these  two 
propositions,  namely,  that  self-fertilisation  is  generally 
injurious,  we  have  abundant  evidence.  The  structure 
of  the  flowers  in  such  plants  as  Lobelia  ramosa,  Digitalis 
purpurea,  &c,  renders  the  aid  of  insects  almost  indis- 
pensable for  their  fertilisation;  and  bearing  in  mind 
the  prepotency  of  pollen  from  a  distinct  individual 
over  that  from  the  same  individual,  such  plants  will 
almost   certainly  have  been  crossed  during  many  or 


Chap.  XII.  GENERAL  RESULTS.  437 

all  previous  generations.  So  it  must  be,  owing  merely 
to  the  prepotency  of  foreign  pollen,  with  cabbages 
and  various  other  plants,  the  varieties  of  which  almost 
invariably  intercross  when  grown  together.  The  same 
inference  may  be  drawn  still  more  surely  with  respect 
to  those  plants,  such  as  Keseda  and  Eschscholtzia, 
which  are  sterile  with  their  own  pollen,  but  fertile 
with  that  from  any  other  individual.  These  several 
plants  must  therefore  have  been  crossed  during  a  long 
series  of  previous  generations,  and  the  artificial  crosses 
in  my  experiments  cannot  have  increased  the  vigour  of 
the  offspring  beyond  that  of  their  progenitors.  There- 
fore the  difference  between  the  self-fertilised  and  crossed 
plants  raised  by  me  cannot  be  attributed  to  the  supe- 
riority of  the  crossed,  but  to  the  inferiority  of  the 
self-fertilised  seedlings,  due  to  the  injurious  effects  of 
self-fertilisation. 

With  respect  to  the  first  proposition,  namely,  that 
cross-fertilisation  is  generally  beneficial,  we  likewise 
have  excellent  evidence.  Plants  of  Ipomoea  were  inter- 
crossed for  nine  successive  generations ;  they  were  then 
again  intercrossed,  and  at  the  same  time  crossed  with  a 
plant  of  a  fresh  stock,  that  is,  one  brought  from  another 
garden ;  and  the  offspring  of  this  latter  cross  were  to 
the  intercrossed  plants  in  height  as  100  to  78,  and  in 
fertility  as  100  to  51.  An  analogous  experiment  with 
Eschscholtzia  gave  a  similar  result,  as  far  as  fertility 
was  concerned.  In  neither  of  these  cases  were  any  of 
the  plants  the  product  of  self-fertilisation.  Plants  of 
Dianthus  were  self- fertilised  for  three  generations,  and 
this  no  doubt  was  injurious  ;  but  when  these  plants 
were  fertilised  by  a  fresh  stock  and  by  intercrossed 
plants  of  the  same  stock,  there  was  a  great  difference 
in  fertility  between  the  two  sets  of  seedlings,  and  some 
difference  in  their  height.     Petunia  offers  a  nearly 


438  GENEKAL  EESULTS.  Chap.  XII 

parallel  case.  With  various  other  plants,  the  wonderful 
effects  of  a  cross  with  a  fresh  stock  may  be  seen  in 
Table  0.  Several  accounts  have  also  been  published* 
of  the  extraordinary  growth  of  seedlings  from  a  cross 
between  two  varieties  of  the  same  species,  some  of  which 
are  known  never  to  fertilise  themselves ;  so  that  here 
neither  self-fertilisation  nor  relationship  even  in  a 
remote  degree  can  have  come  into  play.  We  may 
therefore  conclude  that  the  above  two  propositions  are 
true, — that  cross-fertilisation  is  generally  beneficial 
and  self-fertilisation  injurious  to  the  offspring. 

That  certain  plants,  for  instance,  Viola  tricolor, 
Digitalis  purpurea,  Sarothamnus  scoparius,  Cyclamen 
persicum,  &c,  which  have  been  naturally  cross-fertilised 
for  many  or  all  previous  generations,  should  suffer  to 
an  extreme  degree  from  a  single  act  of  self-fertilisation 
is  a  most  surprising  fact.  Nothing  of  the  kind  has 
been  observed  in  our  domestic  animals  ;  but  then  we 
must  remember  that  the  closest  possible  interbreeding 
with  such  animals,  that  is,  between  brothers  and  sisters, 
cannot  be  considered  as  nearly  so  close  a  union  as  that 
between  the  pollen  and  ovules  of  the  same  flower. 
Whether  the  evil  from  self-fertilisation  goes  on  in- 
creasing during  successive  generations  is  not  as  yet 
known ;  but  we  may  infer  from  my  experiments  that 
the  increase  if  any  is  far  from  rapid.  After  plants  have 
been  propagated  by  self-fertilisation  for  several  genera- 
tions, a  single  cross  with  a  fresh  stock  restores  their 
pristine  vigour ;  and  we  have  a  strictly  analogous 
result  with  our  domestic  animals,  t  The  good  effects 
of  cross-fertilisation  are  transmitted  by  plants  to  the 
next  generation ;    and  judging  from  the  varieties  of 


*  See    'Variation    under    Do-  f  IbuL    ch.  xix.  2nd  edit.  voL 

mestication,'  ch.  xix.  2nd  edit.  vol.       ii.  p.  159. 
ii.  p.  159. 


Chap.  XII.  GENERAL  RESULTS.  439 

the  common  pea,  to  many  succeeding  generations.  But 
this  may  merely  be  that  crossed  plants  of  the  first 
generation  are  extremely  vigorous,  and  transmit  their 
vigour,  like  any  other  character,  to  their  successors. 

Notwithstanding  the  evil  which  many  plants  suffer 
from  self-fertilisation,  they  can  be  thus  propagated 
under  favourable  conditions  for  many  generations,  as 
shown  by  some  of  my  experiments,  and  more  especially 
by  the  survival  during  at  least  half  a  century  of  the 
same  varieties  of  the  common  pea  and  sweet-pea.  The 
same  conclusion  probably  holds  good  with  several  other 
exotic  plants,  which  are  never  or  most  rarely  cross- 
fertilised  in  this  country.  But  all  these  plants,  as  far 
as  they  have  been  tried,  profit  greatly  by  a  cross  with 
a  fresh  stock.  Some  few  plants,  for  instance,  Ophrys 
ajrifera,  have  almost  certainly  been  propagated  in  a 
state  of  nature  for  thousands  of  generations  without 
having  been  once  intercrossed ;  and  whether  they  would 
profit  by  a  cross  with  a  fresh  stock  is  not  known.  But 
such  cases  ought  not  to  make  us  doubt  that  as  a  general 
rule  crossing  is  beneficial,  any  more  than  the  existence 
of  plants  which,  in  a  state  of  nature,  are  propagated 
exclusively  by  rhizomes,  stolons,  &c*  (their  flowers 
never  producing  seeds),  should  make  us  doubt  that 
seminal  generation  must  have  some  great  advantage, 
as  it  is  the  common  plan  followed  by  nature.  Whether 
any  species  has  been  reproduced  asexually  from  a  very 
remote  period  cannot,  of  course,  be  ascertained.  Our 
sole  means  for  forming  any  judgment  on  this  head  is 
the  duration  of  the  varieties  of  our  fruit  trees  which 
have  been  long  propagated  by  grafts  or  buds.  Andrew 
Knight  formerly  maintained  that  under  these  circum- 
stances they  always  become  weakly,  but  this  conclusion 

*  I  have  given  several  cases  in  tion,'  ch.  xviii.  2nd  edit.  vol.  ii. 
say  'Variation  under  Domestica-      p.  152. 


440  GENEKAL  KESULTS.  Chap.  XII 

has  been  warmly  disputed  by  others.  A  recent  and 
competent  judge,  Prof.  Asa  Gray,*  leans  to  the  side 
of  Andrew  Knight,  which  seems  to  me,  from  such 
evidence  as  I  have  been  able  to  collect,  the  more 
probable  view,  notwithstanding  many  opposed  facts. 

The  means  for  favouring  cross-fertilisation  and  pre- 
venting self-fertilisation,  or  conversely  for  favouring 
self-fertilisation  and  preventing  to  a  certain  extent 
cross-fertilisation,  are  wonderfully  diversified;  and  it 
is  remarkable  that  these  differ  widely  in  closely  allied 
plants,! — in  the  species  of  the  same  genus,  and  some- 
times in  the  individuals  of  the  same  species.  It  is 
not  rare  to  find  hermaphrodite  plants  and  others 
with  separated  sexes  within  the  same  genus  ;  and  it  is 
common  to  find  some  of  the  species  dichogamous  and 
others  maturing  their  sexual  elements  simultaneously. 
The  dichogamous  genus  Saxifraga  contains  proter- 
androus  and  proterogynous  species.  |  Several  genera 
include  both  heterostyled  (dimorphic  or  trimorphic 
forms)  and  homostyled  species.  Ophrys  offers  a 
remarkable  instance  of  one  species  having  its  structure 
manifestly  adapted  for  self-fertilisation,  and  other 
species  as  manifestly  adapted  for  cross-fertilisation. 
Some  con-generic  species  are  quite  sterile  and  others 
quite  fertile  with  their  own  pollen.  From  these  several 
causes  we  often  find  within  the  same  genus  species 
which  do  not  produce  seeds,  while  others  produce  an 
abundance,  when  insects  are  excluded.  Some  species 
bear  cleistogene  flowers  which  cannot  be  crossed,  as 
well  as  perfect  flowers,  whilst  others  in  the  same  genus 


*  '  Darwiniana :     Essays    and  tilisation  of  the  Grammese :  '  Mo- 

Eeviews  pertaining  to  Darwinism,'  natsbericht  K.  Akad.  Berlin,'  Oct. 

1876,  p.  338.  1872,  p.  763. 

f    Hildebrand      has      insisted  J  Dr.  Engler,  '  Bot.   Zeitung,' 

strongly    to    this    effect    in  his  1868,  p.  833. 
valuable  observations  on  the  fer- 


Chap.  XII.  GENERAL  RESULTS.  441 

never  produce  cleistogene  flowers.  Some  species  exist 
under  two  forms,  the  one  bearing  conspicuous  flowers 
adapted  for  cross-fertilisation,  the  other  bearing  in- 
conspicuous flowers  adapted  for  self-fertilistion,  whilst 
other  species  in  the  same  genus  present  only  a  single 
form.  Even  with  the  individuals  of  the  same  species, 
the  degree  of  self-sterility  varies  greatly,  as  in  Reseda. 
With  polygamous  plants,  the  distribution  of  the  sexes 
differs  in  the  individuals  of  the  same  species.  The  rela- 
tive period  at  which  the  sexual  elements  in  the  same 
flower  are  mature,  differs  in  the  varieties  of  Pelar- 
gonium ;  and  Carriere  gives  several  cases,*  showing 
that  the  period  varies  according  to  the  temperature  to 
which  the  plants  are  exposed. 

This  extraordinary  diversity  in  the  means  for 
favouring  or  preventing  cross-  and  self-fertilisation  in 
closely  allied  forms,  probably  depends  on  the  results 
of  both  processes  bein<>  highly  beneficial  to  the  species, 
but  directly  opposed  in  many  ways  to  one  another  and 
dependent  on  variable  conditions.  Self-fertilisation 
assures  the  production  of  a  large  supply  of  seeds  ;  and 
the  necessity  or  advantage  of  this  will  be  determined 
by  the  average  length  of  life  of  the  plant,  Avhich  largely 
depends  on  the  amount  of  destruction  suffered  by  the 
seeds  and  seedlings.  This  destruction  follows  from 
the  most  various  and  variable  causes,  such  as  the 
presence  of  animals  of  several  kinds,  and  the  growth 
of  surrounding  plants.  The  possibility  of  cross-fertili- 
sation depends  mainly  on  the  presence  and  number 
of  certain  insects,  often  of  insects  belonging  to  special 
groups,  and  on  the  degree  to  which  they  are  attracted 
to  the  flowers  of  any  particular  species  in  preference  to 
other  flowers, — all  circumstances  likely   to    change. 


*  <Des  Varietes,'  1865,  p.  30. 


442  GENERAL  RESULTS.  Chap.  XIL 

Moreover,  the  advantages  which  follow  from  cross- 
fertilisation  differ  much  in  different  plants,  so  that  it 
is  probable  that  allied  plants  would  often  profit  in 
different  degrees  by  cross-fertilisation.  Under  these 
extremely  complex  and  fluctuating  conditions,  with 
two  somewhat  opposed  ends  to  be  gained,  namely,  the 
safe  propagation  of  the  species  and  the  production  of 
cross-fertilised,  vigorous  offspring,  it  is  not  surprising 
that  allied  forms  should  exhibit  an  extreme  diversity 
in  the  means  which  favour  either  end.  If,  as  there  is 
reason  to  suspect,  self-fertilisation  is  in  some  respects 
beneficial,  although  more  than  counterbalanced  by  the 
advantages  derived  from  a  cross  with  a  fresh  stock,  the 
problem  becomes  still  more  complicated. 

As  I  only  twice  experimented  on  more  than  a  single 
species  in  a  genus,  I  caunot  say  whether  the  crossed 
offspring  of  the  several  species  within  the  same  genus 
differ  in  their  degree  of  superiority  over  their  self- 
fertilised  brethren ;  but  I  should  expect  that  this 
would  often  prove  to  be  the  case  from  what  was 
observed  with  the  two  species  of  Lobelia  and  with  the 
individuals  of  the  same  species  of  Nicotiana.  The 
species  belonging  to  distinct  genera  in  the  same  family 
certainly  differ  in  this  respect.  The  effects  of  cross- 
and  self-fertilisation  may  be  confined  either  to  the 
growth  or  to  the  fertility  of  the  offspring,  but  generally 
extends  to  both  qualities.  There  does  not  seem  to 
exist  any  close  correspondence  between  the  degree  to 
which  the  flowers  of  species  are  adapted  for  cross- 
fertilisation,  and  the  degree  to  which  their  offspring 
profit  by  this  process ;  but  we  may  easily  err  on  this 
head,  as  there  are  two  means  for  ensuring  cross-ferti- 
lisation which  are  not  externally  perceptible,  namely, 
self-sterility  and  the  prepotent  fertilising  influence  of 
pollen  from  another  individual.     Lastly,  it  has  been 


Chap.  XII.  GENERAL   RESULTS.  443 

shown  in  a  former  chapter  that  the  effect  produced  by 
cross  and  self-fertilisation  on  the  fertility  of  the  parent- 
plants  does  not  always  correspond  with  that  produced 
on  the  height,  vigour,  and  fertility  of  their  offspring. 
The  same  remark  applies  to  crossed  and  self-fertilised 
seedlings  when  these  are  used  as  the  parent-plants.  This 
want  of  correspondence  probably  depends,  at  least  in 
part,  on  the  number  of  seeds  produced  being  chiefly 
determined  by  the  number  of  the  pollen-tubes  which 
reach  the  ovules,  and  this  will  be  governed  by  the  re- 
action between  the  pollen  and  the  stigmatic  secretion 
or  tissues;  whereas  the  growth  and  constitutional  vigour 
of  the  offspring  will  be  chiefly  determined,  not  only  by 
the  number  of  pollen-tubes  reaching  the  ovules,  but  by 
the  nature  of  the  reaction  between  the  contents  of  the 
pollen-grains  and  ovules. 

There  are  two  other  important  conclusions  which 
may  be  deduced  from  my  observations :  firstly,  that  the 
advantages  of  cross-fertilisation  do  not  follow  from 
some  mysterious  virtue  in  the  mere  union  of  two 
distinct  individuals,  but  from  such  individuals  having 
been  subjected  during  previous  generations  to  dif- 
ferent conditions,  or  to  their  having  varied  in  a  manner 
commonly  called  spontaneous,  so  that  in  either  case 
their  sexual  elements  have  been  in  some  degree  differ- 
entiated. And  secondly,  that  the  injury  from  self- 
fertilisation  follows  from  the  want  of  such  differentia- 
tion in  the  sexual  elements.  These  two  propositions 
are  fully  established  by  my  experiments.  Thus,  when 
plants  of  the  Ipomoea  and  of  the  Mimulus,  which  had 
been  self-fertilised  for  the  seven  previous  generations 
and  had  been  kept  all  the  time  under  the  same  condi- 
tions, were  intercrossed  one  with  another,  the  offspring 
did  not   profit  in  the  least  by  the  cross.     Mimulus 


444  GENEKAL  EESULTS.  Chap.  XII. 

offers  another  instructive  case,  showing  that  the 
benefit  of  a  cross  depends  on  the  previous  treatment 
of  the  progenitors  :  plants  which  had  been  self-fer- 
tilised for  the  eight  previous  generations  were  crossed 
with  plants  which  had  been  intercrossed  for  the  same 
number  of  generations,  all  having  been  kept  under 
the  same  conditions  as  far  as  possible  ;  seedlings  from 
this  cross  were  grown  in  competition  with  others 
derived  from  the  same  self-fertilised  mother-plant 
crossed  by  a  fresh  stock ;  and  the  latter  seedlings  were 
to  the  former  in  height  as  100  to  52,  and  in  fertility 
as  100  to  4.  An  exactly  parallel  experiment  was 
tried  on  Dianthus,  with  this  difference,  that  the  plants 
had  been  self -fertilised  only  for  the  three  previous  gene- 
rations, and  the  result  was  similar  though  not  so  strongly 
marked.  The  foregoing  two  cases  of  the  offspring  of 
Ipomoea  and  Eschscholtzia,  derived  from  a  cross  with  a 
fresh  stock,  being  as  much  superior  to  the  intercrossed 
plants  of  the  old  stock,  as  these  latter  were  to  the  self- 
fertilised  offspring,  strongly  supports  the  same  conclu- 
sion. A  cross  with  a  fresh  stock  or  with  another  variety 
seems  to  be  always  highly  beneficial,  whether  or 
not  the  mother-plants  have  been  intercrossed  or  self- 
fertilised  for  several  previous  generations.  The  fact 
that  a  cross  between  two  flowers  on  the  same  plant 
does  no  good  or  very  little  good,  is  likewise  a  strong 
corroboration  of  our  conclusion ;  for  the  sexual 
elements  in  the  flowers  on  the  same  plant  can  rarely 
have  been  differentiated,  though  this  is  possible,  as 
flower-buds  are  in  one  sense  distinct  individuals, 
sometimes  varying  and  differing  from  one  another  in 
structure  or  constitution.  Thus  the  proposition  that 
the  benefit  from  cross-fertilisation  depends  on  the 
plants  which  are  crossed  having  been  subjected  during 
previous  generations  to  somewhat  different  conditions, 


Chap.  XII.  GENEKAL  KESULTS.  445 

or  to  their  having  varied  from  some  unknown  cause  as 
if  they  had  been  thus  subjected,  is  securely  fortified  on 
all  sides. 

Before  proceeding  any  further,  the  view  which  has 
been  maintained  by  several  physiologists  must  be 
noticed,  namely,  that  all  the  evils  from  breeding 
animals  too  closely,  and  no  doubt,  as  they  would  say, 
from  the  self-fertilisation  of  plants,  is  the  result  of  the 
increase  of  some  morbid  tendency  or  weakness  of  consti- 
tution common  to  the  closely  related  parents,  or  to 
the  two  sexes  of  hermaphrodite  plants.  Undoubtedly 
injury  has  often  thus  resulted ;  but  it  is  a  vain 
attempt  to  extend  this  view  to  the  numerous  cases 
given  in  my  Tables.  It  should  be  remembered  that  the 
same  mother-plant  was  both  self-fertilised  and  crossed, 
so  that  if  she  had  been  unhealthy  she  would  have 
transmitted  half  her  morbid  tendencies  to  her  crossed 
offspring.  But  plants  appearing  perfectly  healthy, 
some  of  them  growing  wild,  or  the  immediate  offspring 
of  wild  plants,  or  vigorous  common  garden-plants,  were 
selected  for  experiment.  Considering  the  number  of 
species  which  were  tried,  it  is  nothing  less  than  absurd 
to  suppose  that  in  all  these  cases  the  mother-plants, 
though  not  appearing  in  any  way  diseased,  were  weak 
or  unhealthy  in  so  peculiar  a  manner  that  their  self- 
fertilised  seedlings,  many  hundreds  in  number,  were 
rendered  inferior  in  height,  weight,  constitutional 
vigour,  and  fertility  to  their  crossed  offspring.  More- 
over, this  belief  cannot  be  extended  to  the  strongly 
marked  advantages  which  invariably  follow,  as  far  as 
my  experience  serves,  from  intercrossing  the  indivi- 
duals of  the  same  variety  or  of  distinct  varieties,  if 
these  have  been  subjected  during  some  generations  to 
different  conditions. 


446  GENEEAL  RESULTS.  Chap.  XII. 

It  is  obvious  that  the  exposure  of  two  sets  of  plants 
during  several  generations  to  different  conditions  can 
lead  to  no  beneficial  results,  as  far  as  crossing  is  con- 
cerned, unless  their  sexual  elements  are  thus  affected. 
That  every  organism  is  acted  on  to  a  certain  extent  by 
a  change  in  its  environment,  will  not,  I  presume,  be 
disputed.  It  is  hardly  necessary  to  advance  evidence 
on  this  head ;  we  can  perceive  the  difference  between 
individual  plants  of  the  same  species  which  have 
grown  in  somewhat  more  shady  or  sunny,  dry  or  damp 
places.  Plants  which  have  been  propagated  for  some 
generations  under  different  climates  or  at  different 
seasons  of  the  year  transmit  different  constitutions  to 
their  seedlings.  Under  such  circumstances,  the  che- 
mical constitution  of  their  fluids  and  the  nature  of 
their  tissues  are  often  modified.*  Many  other  such 
facts  could  be  adduced.  In  short,  every  alteration  in 
the  function  of  a  part  is  probably  connected  with  some 
corresponding,  though  often  quite  imperceptible  change 
in  structure  or  composition. 

Whatever  affects  an  organism  in  any  way,  likewise 
tends  to  act  on  its  sexual  elements.  We  see  this  in  the 
inheritance  of  newly  acquired  modifications,  such  as 
those  from  the  increased  use  or  disuse  of  a  part,  and 
even  from  mutilations  if  followed  by  disease.f  We 
have  abundant  evidence  how  susceptible  the  repro- 
ductive system  is  to  changed  conditions,  in  the  many 
instances  of  animals  rendered  sterile  by  confinement ; 
so   that  they  will  not  unite,  or  if  they  unite  do  not 

*  Numerous  cases  together  with  the   different   organs  of  animals 

references  are  given  in  my  '  Vari-  are  excited  into  different  degrees 

ation  under   Domestication,'    ch.  of  activity  by  differences  of  tempe- 

xxiii.   2nd   edit.   vol.   ii.   p.   264.  rature  and  food,  and  become  to  a 

With    respect    to    animals,    Mr.  certain  extent  adapted  to  them. 

Biackenridge    has    well     shown  f  'Variation  under  Domestica- 

('  A  Contribution  to  the  Theory  of  tion,'   ch.   xii.   2nd    edit.  vol.   i. 

Diatln  sis,'  Edinburgh,  1889)  that  p.  466. 


Chap.  X1L  GENERAL  RESULTS.  447 

produce  offspring,  though  the  confinement  may  be  far 
from  close ;  and  of  plants  rendered  sterile  by  culti- 
vation. But  hardly  any  cases  afford  more  striking 
evidence  how  powerfully  a  change  in  the  conditions  of 
life  acts  on  the  sexual  elements,  than  those  already 
given,  of  plants  which  are  completely  self-sterile  in 
one  country,  and  when  brought  to  another,  yield,  even 
in  the  first  generation,  a  fair  supply  of  self-fertilised 
seeds. 

But  it  may  be  said,  granting  that  changed  conditions 
act  on  the  sexual  elements,  how  can  two  or  more 
plants  growing  close  together,  either  in  their  native 
country  or  in  a  garden,  be  differently  acted  on,  inasmuch 
as  they  appear  to  be  exposed  to  exactly  the  same 
conditions  ?  Although  this  question  has  been  already 
considered,  it  deserves  further  consideration  under 
several  points  of  view.  In  my  experiments  with 
Digitalis  purpurea,  some  flowers  on  a  wild  plant  were 
self-fertilised,  and  others  were  crossed  with  pollen 
from  another  plant  growing  within  two  or  three  feet's 
distance.  The  crossed  and  self-fertilised  plants  raised 
from  the  seeds  thus  obtained,  produced  flower-stems 
in  number  as  100  to  47,  and  in  average  height  as  100 
to  70.  Therefore  the  cross  between  these  two  plants 
was  highly  beneficial ;  but  how  could  their  sexual 
elements  have  been  differentiated  by  exposure  to 
different  conditions  ?  If  the  progenitors  of  the  two 
plants  had  lived  on  the  same  spot  during  the  last 
score  of  generations,  and  had  never  been  crossed  with 
any  plant  beyond  the  distance  of  a  few  feet,  in  all 
probability  their  offspring  would  have  been  reduced  to 
the  same  state  as  some  of  the  plants  in  my  experiments, 
— such  as  the  intercrossed  plants  of  the  ninth  genera- 
tion of  Ipomoea, — or  the  self-fertilised  plants  of  the 

eighth  generation  of  Mimulus, — or  the  offspring  from 
20 


448  GENERAL  RESULTS.  Chap.  XII. 

flowers  on  the  same  plant, — and  in  this  case  a  cross 
between  the  two  plants  of  Digitalis  would  have  done 
no  good.  But  seeds  are  often  widely  dispersed  by 
natural  means,  and  one  of  the  above  two  plants  or 
one  of  their  ancestors  may  have  come  from  a  distance, 
from  a  more  shady  or  sunny,  dry  or  moist  place,  or  from 
a  different  kind  of  soil  containing  other  organic  or 
inorganic  matter.  We  know  from  the  admirable 
researches  of  Messrs.  Lawes  and  Gilbert*  that  different 
plants  require  and  consume  very  different  amounts  of 
inorganic  matter.  But  the  amount  in  the  soil  would 
probably  not  make  so  great  a  difference  to  the  several 
individuals  of  any  particular  species  as  might  at  first 
be  expected ;  for  the  surrounding  species  with 
different  requirements  would  tend,  from  existing  in 
greater  or  lesser  numbers,  to  keep  each  species  in  a 
sort  of  equilibrium,  with  respect  to  what  it  could  obtain 
from  the  soil.  So  it  would  be  even  with  respect  to 
moisture  during  dry  seasons  ;  and  how  powerful  is  the 
influence  of  a  little  more  or  less  moisture  in  the  soil 
on  the  presence  and  distribution  of  plants,  is  often 
well  shown  in  old  pasture  fields  which  still  retain 
traces  of  former  ridges  and  furrows.  Nevertheless,  as 
the  proportional  numbers  of  the  surrounding  plants  in 
two  neighbouring  places  is  rarely  exactly  the  same,  the 
individuals  of  the  same  species  will  be  subjected  to 
somewhat  different  conditions  with  respect  to  what  they 
can  absorb  from  the  soil.  It  is  surprising  how  the  free 
growth  of  one  set  of  plants  affects  others  growing 
mingled  with  them ;  I  allowed  the  plants  on  rather 
more  than  a  square  yard  of  turf  which  had  been  closely 
mown  for  several  years,  to  grow  up ;  and  nine  species 


*  '  Journal  of  the  Royal  Agricultural  Soc.  of  England,'  vol  xxiy, 
part  i. 


Chap.  XII.  GENERAL  EESULTS.  449 

out  of  twenty  were  thus  exterminated ;  but  whether 
this  was  altogether  due  to  the  kinds  which  grew  up 
robbing  the  others  of  nutriment,  I  do  not  know. 

Seeds  often  lie  dormant  for  several  years  in  the 
ground,  and  germinate  when  brought  near  the  surface 
by  any  means,  as  by  burrowing  animals.  They  would 
probably  be  affected  by  the  mere  circumstance  of  having 
long  lain  dormant ;  for  gardeners  believe  that  the 
production  of  double  flowers  and  of  fruit  is  thus  in- 
fluenced. Seeds,  moreover,  which  were  matured  during 
different  seasons,  will  have  been  subjected  during  the 
whole  course  of  their  development  to  different  degrees 
of  heat  and  moisture. 

It  was  shown  in  the  last  chapter  that  pollen  is  often 
carried  by  insects  to  a  considerable  distance  from 
plant  to  plant.  Therefore  one  of  the  parents  or 
ancestors  of  our  two  plants  of  Digitalis  may  have  been 
crossed  by  a  distant  plant  growing  under  somewhat 
different  conditions.  Plants  thus  crossed  often  pro- 
duce an  unusually  large  number  of  seeds ;  a  striking 
instance  of  this  fact  is  afforded  by  the  Bignonia,  pre- 
viously mentioned,  which  was  fertilised  by  Fritz  Miiller 
with  pollen  from  some  adjoining  plants  and  set  hardly 
any  seed,  but  when  fertilised  with  pollen  from  a  dis- 
tant plant,  was  highly  fertile.  Seedlings  from  a  cross 
of  this  kind  grow  with  great  vigour,  and  transmit  their 
vigour  to  their  descendants.  These,  therefore,  in  the 
struggle  for  life,  will  generally  beat  and  exterminate 
the  seedlings  from  plants  which  have  long  grown  near 
together  under  the  same  conditions,  and  will  thus  tend 
to  spread. 

When  two  varieties  which  present  well-marked 
differences  are  crossed,  their  descendants  in  the  later 
generations  differ  greatly  from  one  another  in  ex- 
ternal characters ;  and  this  is  due  to  the  augmentation 


450  GENEEAL  EESULTS.  Chap.  XII, 

or  obliteration  of  some  of  these  characters,  and  to 
the  reappearance  of  former  ones  through  reversion ; 
and  so  it  will  be,  as  we  may  feel  almost  sure,  with  any- 
slight  differences  in  the  constitution  of  their  sexual 
elements.  Anyhow,  my  experiments  indicate  that 
crossing  plants  which  have  been  long  subjected  to 
almost  though  not  quite  the  same  conditions,  is  the 
most  powerful  of  all  the  means  for  retaining  some 
degree  of  differentiation  in  the  sexual  elements,  as 
shown  by  the  superiority  in  the  later  generations  of  the 
intercrossed  over  the  self-fertilised  seedlings.  Never- 
theless, the  continued  intercrossing  of  plants  thus 
treated  does  tend  to  obliterate  such  differentiation,  as 
may  be  inferred  from  the  lessened  benefit  derived  from 
intercrossing  such  plants,  in  comparison  with  that  from 
a  cross  with  a  fresh  stock.  It  seems  probable,  as  I  may 
add,  that  seeds  have  acquired  their  endless  curious 
adaptations  for  wide  dissemination,  *  not  only  that  the 
seedlings  should  thus  be  enabled  to  find  new  and  fitting 
homes,  but  that  the  individuals  which  have  been  long 
subjected  to  the  same  conditions  should  occasionally 
intercross  with  a  fresh  stock. 

From  the  foregoing  several  considerations  we  may, 
I  think,  conclude  that  in  the  above  case  of  the  Digitalis, 
and  even  in  that  of  plants  which  have  grown  for 
thousands  of  generations  in  the  same  district,  as  must 
often  have  occurred  with  species  having  a  much 
restricted  range,  we  are  apt  to  over-estimate  the 
degree  to  which  the  individuals  have  been  subjected 
to  absolutely  the  same  conditions.  There  is  at  least 
no  difficulty  in  believing  that  such  plants  have  been 
subjected  to  sufficiently  distinct  conditions  to  differ- 
entiate their  sexual  elements ;  for  we  know  that  a  plant 

*  See  Prof.  Hildebrand's  excellent  treatise,  *  Verbreitungsmittel  dei 
Pflaiizen,'  1873. 


Chap.  XII.  GENERAL   RESULTS.  451 

propagated  for  some  generations  in  another  garden  in 
the  same  district  serves  as  a  fresh  stock  and  has  high 
fertilising  powers.  The  curions  cases  of  plants  which 
can  fertilise  and  be  fertilised  by  any  other  individual 
of  the  same  species,  but  are  altogether  sterile  with  their 
own  pollen,  become  intelligible,  if  the  view  here  pro- 
pounded is  correct,  namely,  that  the  individuals  of  the 
same  species  growing  in  a  state  of  nature  near  together, 
have  not  really  been  subjected  during  several  previous 
generations  to  quite  the  same  conditions. 

Some  naturalists  assume  that  there  is  an  innate 
tendency  in  all  beings  to  vary  and  to  advance  in 
organisation,  independently  of  external  agencies ;  and 
they  would,  I  presume,  thus  explain  the  slight 
differences  which  distinguish  all  the  individuals  of  the 
same  species  both  in  external  characters  and  in  con- 
stitution, as  well  as  the  greater  differences  in  both 
respects  between  nearly  allied  varieties.  No  two 
individuals  can  be  found  quite  alike ;  thus  if  we  sow  a 
number  of  seeds  from  the  same  capsule  under  as  nearly 
as  possible  the  same  conditions,  they  germinate  at 
different  rates  and  grow  more  or  less  vigorously.  They 
resist  cold  and  other  unfavourable  conditions  differently. 
They  would  in  all  probability,  as  we  know  to  be  the 
case  with  animals  of  the  same  species,  be  somewhat 
differently  acted  on  by  the  same  poison,  or  by  the  same 
disease.  They  have  different  powers*  of  transmitting 
their  characters  to  their  offspring ;  and  many  analogous 
facts  could  be  given.  Now,  if  it  were  true  that 
plants  growing  near  together  in  a  state  of  nature  had 
been  subjected  during  many  previous  generations  to 
absolutely  the  same  conditions,  such  differences  as  those 
just  specifi.d  would  be  quite  inexplicable ;  but  they 


Vilmorin,  as  quoted  by  Verlot,  '  Des  Varietes,'  pp.  32,  38,  39. 


452  GENERAL  RESULTS.  Chap.  XII. 

are  to  a  certain  extent  intelligible  in  accordance  with 
the  views  just  advanced. 

As  most  of  the  plants  on  which  I  experimented 
were  grown  in  my  garden  or  in  pots  under  glass,  a  few 
words  must  be  added  on  the  conditions  to  which  they 
were  exposed,  as  well  as  on  the  effects  of  cultivation. 
When  a  species  is  first  brought  under  culture,  it  may 
or  may  not  be  subjected  to  a  change  of  climate,  but  it 
is  always  grown  in  ground  broken  up,  and  more  or  less 
manured  ;  it  is  also  saved  from  competition  with  other 
plants.  The  paramount  importance  of  this  latter 
circumstance  is  proved  by  the  multitude  of  species 
which  flourish  and  multiply  in  a  garden,  but  cannot 
exist  unless  they  are  protected  from  other  plants. 
When  thus  saved  from  competition  they  are  able  to 
get  whatever  they  require  from  the  soil,  probably 
often  in  excess  ;  and  they  are  thus  subjected  to  a  great 
change  of  conditions.  It  is  probably  in  chief  part 
owing  to  this  cause  that  all  plants  with  rare  excep- 
tions vary  after  being  cultivated  for  some  generations. 
The  individuals  which  have  already  begun  to  vary 
will  intercross  one  with  another  by  the  aid  of  insects ; 
and  this  accounts  for  the  extreme  diversity  of  character 
which  many  of  our  long  cultivated  plants  exhibit. 
But  it  should  be  observed  that  the  result  will  be 
largely  determined  by  the  degree  of  their  variability 
and  by  the  frequency  of  the  intercrosses  ;  for  if  a  plant 
varies  very  little,  like  most  species  in  a  state  of  nature, 
frequent  intercrosses  tend  to  give  uniformity  of 
character  to  it. 

I  have  attempted  to  show  that  with  plants  growing 
naturally  in  the  same  district,  except  in  the  unusual 
case  of  each  individual  being  surrounded  by  exactly 
the  same  proportional  numbers  of  other  species  having 
certain  powers  of  absorption,  each  will  be  subjected  to 


Chap.  XII.  GENEKAL  EESULTS.  453 

slightly  different  conditions.  This  does  not  apply  to 
the  individuals  of  the  same  species  when  cultivated  in 
cleared  ground  in  the  same  garden.  But  if  their 
flowers  are  visited  by  insects,  they  will  intercross  ;  and 
this  will  give  to  their  sexual  elements  during  a 
considerable  number  of  generations  a  sufficient  amount 
of  differentiation  for  a  cross  to  be  beneficial.  More- 
over, seeds  are  frequently  exchanged  or  procured  from 
other  gardens  having  a  different  kind  of  soil ;  and  the 
individuals  of  the  same  cultivated  species  will  thus  be 
subjected  to  a  change  of  conditions.  If  the  flowers  are 
not  visited  by  our  native  insects,  or  very  rarely  so, 
as  in  the  case  of  the  common  and  sweet  pea,  and 
apparently  in  that  of  the  tobacco  when  kept  in  a 
hothouse,  any  differentiation  in  the  sexual  elements 
caused  by  intercrosses  will  tend  to  disappear.  This 
appears  to  have  occurred  with  the  plants  just 
mentioned,  for  they  were  not  benefited  by  being 
crossed  one  with  another,  though  they  were  greatly 
benefited  by  a  cross  with  a  fresh  stock. 

I  have  been  led  to  the  views  just  advanced  with 
respect  to  the  causes  of  the  differentiation  of  the  sexual 
elements  and  of  the  variability  of  our  garden  plants, 
by  the  results  of  my  various  experiments,  and  more 
especially  by  the  four  cases  in  which  extremely  incon- 
stant species,  after  having  been  self-fertilised  and 
grown  under  closely  similar  conditions  for  several 
generations,  produced  flowers  of  a  uniform  and  constant 
tint.  These  conditions  were  nearly  the  same  as  those 
to  which  plants,  growing  in  a  garden  clear  of  weeds, 
are  subjected,  if  they  are  propagated  by  self-fertilised 
seeds  on  the  same  spot.  The  plants  in  pots  were, 
however,  exposed  to  less  severe  fluctuations  of  climate 
than  those  out  of  doors ;  but  their  conditions,  though 
closely  uniform  for  all   the   individuals  of  the   same 


454  GENEEAL  EESULTS.  Chap.  XII. 

generation,  differed  somewhat  in  the  successive  gene- 
rations. Now,  under  these  circumstances,  the  sexual 
elements  of  the  plants  which  were  intercrossed  in  each 
generation  retained  sufficient  differentiation  during 
several  years  for  their  offspring  to  be  superior  to 
the  self-fertilised,  but  this  superiority  gradually  and 
manifestly  decreased,  as  was  shown  by  the  difference 
in  the  result  between  a  cross  with  one  of  the  inter- 
crossed plants  and  with  a  fresh  stock.  These  inter- 
crossed plants  tended  also  in  a  few  cases  to  become 
somewhat  more  uniform  in  some  of  their  external  cha- 
racters than  they  were  at  first.  With  respect  to  the 
plants  which  were  self-fertilised  in  each  generation, 
their  sexual  elements  apparently  lost,  after  some  years, 
all  differentiation,  for  a  cross  between  them  did  no 
more  good  than  a  cross  between  the  flowers  on  the 
same  plant.  But  it  is  a  still  more  remarkable  fact,  that 
although  the  seedlings  of  Mimulus,  Ipomcea,  Dianthus, 
and  Petunia  which  were  first  raised,  varied  excessively  in 
the  colour  of  their  flowers,  their  offspring,  after  being 
self-fertilised  and  grown  under  uniform  conditions  for 
some  generations,  bore  flowers  almost  as  uniform  in 
tint  as  those  on  a  natural  species.  In  one  case  also 
the  plants  themselves  became  remarkably  uniform  in 
height. 

The  conclusion  that  the  advantages  of  a  cross 
depend  altogether  on  the  differentiation  of  the  sexual 
elements,  harmonises  perfectly  with  the  fact  that  an 
occasional  and  slight  change  in  the  conditions  of  life 
is  beneficial  to  all  plants  and  animals.*  But  the 
offspring  from  a  cross  between  organisms  which  have 
been  exposed  to  different  conditions,  profit  in  an  in- 
comparably higher  degree  than  do  young  or  old  beings 

*  I  have  given  sufficient  evi-  ation  under  Domestication,'  ch. 
dence  on  this  head  in  my  '  Vari-      xviii.  vol.  ii.  2nd  edit.  p.  127. 


Chap.  XIL  GENERAL  RESULTS.  455 

from  a  mere  change  in  their  conditions.  In  this 
latter  case  we  never  see  anything  like  the  effect 
which  generally  follows  from  a  cross  with  another 
individual,  especially  from  a  cross  with  a  fresh  stock. 
This  might,  perhaps,  have  been  expected,  for  the 
blending  together  of  the  sexual  elements  of  two  dif- 
ferentiated beings  will  affect  the  whole  constitution  at 
a  very  early  period  of  life,  whilst  the  organisation  is 
highly  flexible.  We  have,  moreover,  reason  to  believe 
that  changed  conditions  generally  act  differently  on 
the  several  parts  or  organs  of  the  same  individual  ;* 
and  if  we  may  further  believe  that  these  now  slightly 
differentiated  parts  react  on  one  another,  the  harmony 
between  the  beneficial  effects  on  the  individual  due  to 
changed  conditions,  and  those  due  to  the  interaction  of 
differentiated  sexual  elements,  becomes  still  closer. 

That  wonderfully  accurate  observer,  Sprengel,  who 
first  showed  how  important  a  part  insects  play  in  the 
fertilisation  of  flowers,  called  his  book  '  The  Secret 
of  Nature  Displayed ; '  yet  he  only  occasionally  saw 
that  the  object  for  which  so  many  curious  and  beautiful 
adaptations  have  been  acquired,  was  the  cross-fertilisa- 
tion of  distinct  plants ;  and  he  knew  nothing  of  the 
benefits  which  the  offspring  thus  receive  in  growth, 
vigour,  and  fertility.  But  the  veil  of  secrecy  is  as 
yet  far  from  lifted ;  nor  will  it  be,  until  we  can  say 
why  it  is  beneficial  that  the  sexual  elements  should 
be  differentiated  to  a  certain  extent,  and  why,  if  the 
differentiation  be  carried  still  further,  injury  follows. 
It  is  an  extraordinary  fact  that  with  many  species, 
flowers  fertilised  with  their  own  pollen  are  either 
absolutely  or  in  some  degree  sterile ;  if  fertilised  with 

*  See,  for  instance,  Brackenridge,  '  Theory  of  Diathesis,'  Edinburgh, 
'869. 


456  GENERAL  EESULTS.  Chap.  XII. 

pollen  from  another  flower  on  the  same  plant,  they  are 
sometimes,  though  rarely,  a  little  more  fertile;  if 
fertilised  with  pollen  from  another  individual  or  variety 
of  the  same  species,  they  are  fully  fertile ;  but  if 
with  pollen  from  a  distinct  species,  they  are  sterile 
in  all  possible  degrees,  until  utter  sterility  is  reached. 
We  thus  have  a  long  series  with  absolute  sterility  at 
the  two  ends ; — at  one  end  due  to  the  sexual  elements 
not  having  been  sufficiently  differentiated,  and  at  the 
other  end  to  their  having  been  differentiated  in  too 
great  a  degree,  or  in  some  peculiar  manner. 

The  fertilisation  of  one  of  the  higher  plants  depends, 
in  the  first  place,  on  the  mutual  action  of  the  pollen- 
grains  and  the  stigmatic  secretion  or  tissues,  and  after- 
wards on  the  mutual  action  of  the  contents  of  the 
pollen-grains  and  ovules.  Both  actions,  judging  from 
the  increased  fertility  of  the  parent-plants  and  from  the 
increased  powers  of  growth  in  the  offspring,  are  favoured 
by  some  degree  of  differentiation  in  the  elements 
which  interact  and  unite  so  as  to  form  a  new  being. 
Here  we  have  some  analogy  with  chemical  affinity  or 
attraction,  which  comes  into  play  only  between  atoms 
or  molecules  of  a  different  nature.  As  Prof.  Miller 
remarks :  "  Generally  speaking,  the  greater  the  dif- 
ference in  the  properties  of  two  bodies,  the  more  intense 
is  their  tendency  to  mutual  chemical  action.  .  .  .  But 
between  bodies  of  a  similar  character  the  tendency  to 
unite  is  feeble."*  This  latter  proposition  accords  well 
with  the  feeble  effects  of  a  plant's  own  pollen  on  the 
fertility  of  the  mother-plant  and  on  the  growth  of  the 
offspring  ;  and  the  former  proposition  accords  well  with 
the  powerful  influence  in  both  ways  of  pollen  from  an 

*  '  Elements  of  Chemistry,'  4th  views  with  respect  to  chemical 
edit.  1867,  part  i.  p.  11.  Dr.  affinity  are  generally  accepted  by 
Frankland  informs  me  that  similar       chemists. 


Chap.  XIL  GENERAL  EESULTS.  457 

individual  which  has  been  differentiated  by  exposure 
to  changed  conditions,  or  by  so-called  spontaneous 
variation.  But  the  analogy  fails  when  we  turn  to  the 
negative  or  weak  effects  of  pollen  from  one  species  on 
a  distinct  species  ;  for  although  some  substances  which 
are  extremely  dissimilar,  for  instance,  carbon  and 
chlorine,  have  a  very  feeble  affinity  for  each  other, 
yet  it  cannot  be  said  that  the  weakness  of  the  affinity 
depends  in  such  cases  on  the  extent  to  which  the 
substances  differ.  It  is  not  known  why  a  certain 
amount  of  differentiation  is  necessary  or  favourable 
for  the  chemical  affinity  or  union  of  two  substances, 
any  more  than  for  the  fertilisation  or  union  of  two 
organisms. 

Mr.  Herbert  Spencer  has  discussed  this  whole  subject 
at  great  length,  and  after  stating  that  all  the  forces 
throughout  nature  tend  towards  an  equilibrium, 
remarks,  "  that  the  need  of  this  union  of  sperm - 
cell  and  germ-cell  is  the  need  for  overthrowing  this 
equilibrium  and  re-establishing  active  molecular 
change  in  the  detached  germ — a  result  which  is 
probably  effected  by  mixing  the  slightly-different 
physiological  units  of  slightly-different  individuals."* 
But  we  must  not  allow  this  highly  generalised  view,  or 
the  analogy  of  chemical  affinity,  to  conceal  from  us 
our  ignorance.  We  do  not  know  what  is  the  nature  or 
degree  of  the  differentiation  in  the  sexual  elements 
which  is  favourable  for  union,  and  what  is  injurious  foe 
union,  as  in  the  case  of  distinct  species.     We  cannot 


*  'Principles  of  Biology,'  vol. i.  changes  in    the    conditions  and 

p    274,  1864.     In  my  '  Origin  of  from  crossing  widely  distinct  forms 

Species,'    published    in    1859,    I  (i.e.,  species),  as  a  series  of  facts 

spoke   of  the   good  effects  from  "  connected     together    by    some 

slight  changes  in  the  condition  of  common     but     unknown    bond, 

life   and    from   cross-fertilisation,  which   is  essentially   related    to 

and  of  the  evil  effects  from  great  the  principle  of  life." 


458  GENERAL  RESULTS.  Chap.  XIL 

say  why  the  individuals  of  certain  species  profit  greatly, 
and  others  very  little  by  being  crossed.  There  are  some 
few  species  which  have  been  self-fertilised  for  a  vast 
number  of  generations,  and  yet  are  vigorous  enough 
to  compete  successfully  with  a  host  of  surrounding 
plants.  Highly  self-fertile  varieties  sometimes  arise 
among  plants  which  have  been  self-fertilised  and 
grown  under  uniform  conditions  during  several  gene- 
rations. We  can  form  no  conception  why  the 
advantage  from  a  cross  is  sometimes  directed  exclu- 
sively to  the  vegetative  system,  and  sometimes  to  the 
reproductive  system,  but  commonly  to  both.  It  is 
equally  inconceivable  why  some  individuals  of  the  same 
species  should  be  sterile,  whilst  others  are  fully  fertile 
with  their  own  pollen ;  why  a  change  of  climate  should 
either  lessen  or  increase  the  sterility  of  self-sterile 
species;  and  why  the  individuals  of  some  species  should 
be  even  more  fertile  with  pollen  from  a  distinct  species 
than  with  their  own  pollen.  And  so  it  is  with  many 
other  facts,  which  are  so  obscure  that  we  stand 
in  awe  before  the  mystery  of  life. 

Under  a  practical  point  of  view,  agriculturists  and 
horticulturists  may  learn  something  from  the  conclu- 
sions at  which  we  have  arrived.  Firstly,  we  see  that 
the  injury  from  the  close  breeding  of  animals  and 
from  the  self-fertilisation  of  plants,  does  not  necessarily 
depend  on  any  tendency  to  disease  or  weakness  of  con- 
stitution common  to  the  related  parents,  and  only 
indirectly  on  their  relationship,  in  so  far  as  they  are 
apt  to  resemble  each  other  in  all  respeets,  including 
their  sexual  nature.  And,  secondly,  that  the  advantages 
of  cross-fertilisation  depend  on  the  sexual  elements  of 
the  parents  having  become  in  some  degree  differentiated 
by   the   exposure   of    their   progenitors    to    different 


Chap.  XII.  GENERAL   RESULTS.  459 

conditions,  or  from  their  having  intercrossed  with 
individuals  thus  exposed,  or,  lastly,  from  what  we  call 
in  our  ignorance  spontaneous  variation.  He  therefore 
who  wishes  to  pair  closely  related  animals  ought  to 
keep  them  under  conditions  as  different  as  possible. 
Some  few  breeders,  guided  by  their  keen  powers  of 
observation,  have  acted  on  this  principle,  and  have  kept 
stocks  of  the  same  animals  at  two  or  more  distant  and 
differently  situated  farms.  They  have  then  coupled 
the  individuals  from  these  farms  with  excellent  results.* 
This  same  plan  is  also  unconsciously  followed  whenever 
the  males,  reared  in  one  place,  are  let  out  for  propaga- 
tion to  breeders  in  other  places.  As  some  kinds  of 
plants  suffer  much  more  from  self-fertilisation  than  do 
others,  so  it  probably  is  with  animals  from  too  close 
interbreeding.  The  effects  of  close  interbreeding  on 
animals,  judging  again  from  plants,  would  be  dete- 
rioration in  general  vigour,  including  fertility,  with  no 
necessary  loss  of  excellence  of  form ;  and  this  seems 
to  be  the  usual  result. 

It  is  a  common  practice  with  horticulturists  to 
obtain  seeds  from  another  place  having  a  very  dif- 
ferent soil,  so  as  to  avoid  raising  plants  for  a  long 
succession  of  generations  under  the  same  conditions ; 
but  with  all  the  species  which  freely  intercross  by  the 
aid  of  insects  or  the  wind,  it  would  be  an  incomparably 
better  plan  to  obtain  seeds  of  the  required  variety, 
which  had  been  raised  for  some  generations  under  as 
different  conditions  as  possible,  and  sow  them  in 
alternate  rows  with  seeds  matured  in  the  old  garden. 
The  two  stocks  would  then  intercross,  with  a  thorough 
blending  of  their  whole  organisations,  and  with  no  loss 
of  purity  to  the  variety ;  and  this  would  yield  far  more 

*  '  Variation  of  Animals   and      xvii.  2nd  edit.  vol.  ii.  pp.  98,  105. 
Plants  under  Domestication,  ch. 


460  GENERAL  RESULTS.  Chap.  XIL 

favourable  results  than  a  mere  exchange  of  seeds.  We 
have  seen  in  my  experiments  how  wonderfully  the 
offspring  profited  in  height,  weight,  hardiness,  and  fer- 
tility, by  crosses  of  this  kind.  For  instance,  plants  of 
Ipomoea  thus  crossed  were  to  the  intercrossed  plants 
of  the  same  stock,  with  which  they  grew  in  competition, 
as  100  to  78  in  height,  and  as  100  to  51  in  fertility ; 
and  plants  of  Eschscholtzia  similarly  compared  were 
as  100  to  45  in  fertility.  In  comparison  with  self- 
fertilised  plants  the  results  are  still  more  striking ; 
thus  cabbages  derived  from  a  cross  with  a  fresh  stock 
were  to  the  self-fertilised  as  100  to  22  in  weight. 

Florists  may  learn  from  the  four  cases  which  have 
been  fully  described,  that  they  have  the  power  of  fixing 
each  fleeting  variety  of  colour,  if  they  will  fertilise  the 
flowers  of  the  desired  kind  with  their  own  pollen  for 
half-a-dozen  generations,  and  grow  the  seedlings  under 
the  same  conditions.  But  a  cross  with  any  other  in- 
dividual of  the  same  variety  must  be  carefully  pre- 
vented, as  each  has  its  own  peculiar  constitution.  After 
a  dozen  generations  of  self-fertilisation,  it  is  probable 
that  the  new  variety  would  remain  constant  even  if 
grown  under  somewhat  different  conditions ;  and  there 
would  no  longer  be  any  necessity  to  guard  against  inter- 
crosses between  the  individuals  of  the  same  variety. 

With  respect  to  mankind,  my  son  G-eorge  has  en- 
deavoured to  discover  by  a  statistical  investigation* 
whether  the  marriages  of  first  cousins  are  at  all  in- 
jurious, although  this  is  a  degree  of  relationship 
which  would  not  be  objected  to  in  our  domestic 
animals ;  and  he  has  come  to  the  conclusion  from  his 
own  researches  and  those  of  Dr.  Mitchell  that  the 
evidence  as  to  any  evil  thus  caused  is  conflicting,  but 

*  'Journal  of  Statistical  Soc'      nightly  Review,'  June  1875. 
June  1875,   p.   153;   and  'Fort- 


Chap.  XII.  GENEEAL  RESULTS.  461 

on  the  whole  points  to  its  being  very  small.  From  the 
facts  given  in  this  volume  we  may  infer  that  with 
mankind  the  marriages  of  nearly  related  persons,  some 
of  whose  parents  and  ancestors  had  lived  under  very 
different  conditions,  would  be  much  less  injurious  than 
that  of  persons  who  had  always  lived  in  the  same 
place  and  followed  the  same  habits  of  life.  Nor  can  I 
see  reason  to  doubt  that  the  widely  different  habits  of 
life  of  men  and  women  in  civilised  nations,  especially 
amongst  the  upper  classes,  would  tend  to  counter- 
balance any  evil  from  marriages  between  healthy  and 
somewhat  closely  related  persons. 

Under  a  theoretical  point  of  view  it  is  some  gain  to 
science  to  know  that  numberless  structures  in  her- 
maphrodite plants,  and  probably  in  hermaphrodite 
animals,  are  special  adaptations  for  securing  an  occa- 
sional cross  between  two  individuals;  and  that  the 
advantages  from  such  a  cross  depend  altogether  on  the 
beings  which  are  united,  or  their  progenitors,  having 
had  their  sexual  elements  somewhat  differentiated,  so 
that  the  embyro  is  benefited  in  the  same  manner  as  is 
a  mature  plant  or  animal  by  a  slight  change  in  its 
conditions  of  life,  although  in  a  much  higher  degree. 

Another  and  more  important  result  may  be  deduced 
from  my  observations.  Eggs  and  seeds  are  highly 
serviceable  as  a  means  of  dissemination,  but  we  now 
know  that  fertile  eggs  can  be  produced  without  the 
aid  of  the  male.  There  are  also  many  other  methods 
by  which  organisms  can  be  propagated  asexually. 
Why  then  have  the  two  sexes  been  developed,  and 
why  do  males  exist  which  cannot  themselves  produce 
offspring  ?  The  answer  lies,  as  I  can  hardly  doubt,  in 
the  great  good  which  is  derived  from  the  fusion  of  two 
somewhat   differentiated    individuals ;    and   with   the 


462  GENEKAL  EESTJLTS.  Chap.  XH. 

oxception  of  the  lowest  organisms  this  is  possible  only 
by  means  of  the  sexual  elements,  these  consisting  of 
cells  separated  from  the  body,  containing  the  germs  of 
every  part,  and  capable  of  being  fused  completely 
together. 

It  has  been  shown  in  the  present  volume  that  the 
offspring  from  the  union  of  two  distinct  individuals, 
especially  if  their  progenitors  have  been  subjected  to 
very  different  conditions,  have  an  immense  advantage 
in  height,  weight,  constitutional  vigour  and  fertility 
over  the  self-fertilised  offspring  from  one  of  the  same 
parents.  And  this  fact  is  amply  sufficient  to  account 
for  the  development  of  the  sexual  elements,  that  is,  for 
the  genesis  of  the  two  sexes. 

It  is  a  different  question  why  the  two  sexes  are 
sometimes  combined  in  the  same  individual  and  are 
sometimes  separated.  As  with  many  of  the  lowest 
plants  and  animals  the  conjugation  of  two  individuals 
which  are  either  quite  similar  or  in  some  degree  dif- 
ferent, is  a  common  phenomenon,  it  seems  probable, 
as  remarked  in  the  last  chapter,  that  the  sexes  were 
primordially  separate.  The  individual  which  receives 
the  contents  of  the  other,  may  be  called  the  female ; 
and  the  other,  which  is  often  smaller  and  more  loco- 
motive, may  be  called  the  male ;  though  these  sexual 
names  ought  hardly  to  be  applied  as  long  as  the 
whole  contents  of  the  two  forms  are  blended  into  one. 
The  object  gained  by  the  two  sexes  becoming  united 
in  the  same  hermaphrodite  form  probably  is  to  allow 
of  occasional  or  frequent  self-fertilisation,  so  as  to 
ensure  the  propagation  of  the  species,  more  especially 
in  the  case  of  organisms  affixed  for  life  to  the  same 
spot.  There  does  not  seem  to  be  any  great  difficulty 
in  understanding  how  an  organism,  formed  by  the  con- 
jugation of  two  individuals  which  represented  the  two 


Chap.  XII.  GENEKAL  EESULTS.  463 

incipient  sexes,  might  have  given  rise  by  budding  first 
to  a  monoecious  and  then  to  an  hermaphrodite  form ; 
and  in  the  case  of  animals  even  without  budding  to 
an  hermaphrodite  form,  for  the  bilateral  structure  of 
animals  perhaps  indicates  that  they  were  aboriginally 
formed  by  the  fusion  of  two  individuals. 

It  is  a  more  difficult  problem  why  some  plants  and 
apparently  all  the  higher  animals,  after  becoming  her- 
maphrodites, have  since  had  their  sexes  re-separated. 
This  separation  has  been  attributed  by  some  natural- 
ists to  the  advantages  which  follow  from  a  division  of 
physiological  labour.  The  principle  is  intelligible 
when  the  same  organ  has  to  perform  at  the  same  time 
diverse  functions  ;  but  it  is  not  obvious  why  the  male 
and  female  glands  when  placed  in  different  parts  of 
the  same  compound  or  simple  individual,  should  not 
perform  their  functions  equally  well  as  when  placed  in 
two  distinct  individuals.  In  some  instances  the  sexes 
may  have  been  re-separated  for  the  sake  of  preventing 
too  frequent  self-fertilisation ;  but  this  explanation 
does  not  seem  probable,  as  the  same  end  might  have 
been  gained  by  other  and  simpler  means,  for  instance 
dichogamy.  It  may  be  that  the  production  of  the 
male  and  female  reproductive  elements  and  the 
maturation  of  the  ovules  was  too  great  a  strain  and 
expenditure  of  vital  force  for  a  single  individual  to 
withstand,  if  endowed  with  a  highly  complex  organi- 
sation ;  and  that  at  the  same  time  there  was  no  need 
for  all  the  individuals  to  produce  young,  and  conse- 
quently that  no  injury,  on  the  contrary,  good  resulted 
from  half  of  them,  or  the  males,  failing  to  produce 
offspring. 

There  is  another  subject  on  which  some  light  is 
thrown  by  the  facts  given  in  this  volume,  namely, 
hybridisation.     It    is    notorious    that   when    distinct 


464  GENERAL   RESULTS.  Chap.  XII. 

species  of  plants  are  crossed,  they  produce  with  the 
rarest  exceptions  fewer  seeds  than  the  normal  number. 
This  unproductiveness  varies  in  different  species  up  to 
sterility  so  complete  that  not  even  an  empty  capsule 
is  formed ;  and  all  experimentalists  have  found  that 
it  is  much  influenced  by  the  conditions  to  which  the 
crossed  species  are  subjected.  The  pollen  of  each 
species  is  strongly  prepotent  over  that  of  any  other 
species,  so  that  if  a  plant's  own  pollen  is  placed  on 
the  stigma  some  time  after  foreign  pollen  has  been 
applied  to  it,  any  effect  from  the  latter  is  quite  obli- 
terated. It  is  also  notorious  that  not  only  the  parent 
species,  but  the  hybrids  raised  from  them  are  more  or 
less  sterile ;  and  that  their  pollen  is  often  in  a  more 
or  less  aborted  condition.  The  degree  of  sterility  of 
various  hybrids  does  not  always  strictly  correspond 
with  the  degree  of  difficulty  in  uniting  the  parent 
forms.  When  hybrids  are  capable  of  breeding  inter  se, 
their  descendants  are  more  or  less  sterile,  and  they 
often  become  still  more  sterile  in  the  later  generations  ; 
but  then  close  interbreeding  has  hitherto  been  practised 
in  all  such  cases.  The  more  sterile  hybrids  are  some- 
times much  dwarfed  in  stature,  and  have  a  feeble  con- 
stitution. Other  facts  could  be  given,  but  these  will 
suffice  for  us.  Naturalists  formerly  attributed  all  these 
results  to  the  difference  between  species  being  funda- 
mentally distinct  from  that  between  the  varieties  of 
the  same  species ;  and  this  is  still  the  verdict  of  some 
naturalists. 

The  results  of  my  experiments  in  self-fertilising  and 
cross-fertilising  the  individuals  or  the  varieties  of  the 
same  species,  are  strikingly  analogous  with  those  just 
given,  though  in  a  reversed  manner.  With  the  majority 
of  species  flowers  fertilised  with  their  own  pollen  yield 
fewer,  sometimes  much  fewer  seeds,  than  those  ferti- 


Cha.k  XII.  GENERAL  RESULTS.  465 

lised  with  pollen  from  another  individual  or  variety. 
Some  self-fertilised  flowers  are  absolutely  sterile ;  but 
the  degree  of  their  sterility  is  largely  determined  by 
the  conditions  to  which  the  parent  plants  have  been 
exposed,  as  was  well  exemplified  in  the  case  of  Esch- 
scholtzia  and  Abutilon.  The  effects  of  pollen  from  the 
same  plant  are  obliterated  by  the  prepotent  influence 
of  pollen  from  another  individual  or  variety,  although 
the  latter  may  have  been  placed  on  the  stigma  some 
hours  afterwards.  The  offspring  from  self-fertilised 
flowers  are  themselves  more  or  less  sterile,  sometimes 
highly  sterile,  and  their  pollen  is  sometimes  in  an 
imperfect  condition ;  but  I  have  not  met  with  any  case 
of  complete  sterility  in  self-fertilised  seedlings,  as  is 
so  common  with  hybrids.  The  degree  of  their  sterility 
does  not  correspond  with  that  of  the  parent-plants  when 
first  self-fertilised.  The  offspring  of  self-fertilised 
plants  suffer  in  stature,  weight,  and  constitutional 
vigour  more  frequently  and  in  a  greater  degree  than 
do  the  hybrid  offspring  of  the  greater  number  of 
crossed  species.  Decreased  height  is  transmitted  to 
the  next  generation,  but  I  did  not  ascertain  whether 
this  applies  to  decreased  fertility. 

I  have  elsewhere  shown  *  that  by  uniting  in  various 
ways  dimorphic  or  trimorphic  heterostyled  plants, 
which  belong  to  the  same  undoubted  species,  we  get 
another  series  of  results  exactly  parallel  with  those 
from  crossing  distinct  species.  Plants  illegitimately 
fertilised  with  pollen  from  a  distinct  plant  belonging 
to  the  same  form,  yield  fewer,  often  much  fewer  seeds, 
than  they  do  when  legitimately  fertilised  with  pollen 
from  a  plant  belonging  to  a  distinct  form.  They  some- 
times yield  no  seed,  not  even  an  empty  capsule,  like 


'  Journal  Linu.  Sac.  Bot.'  vol.  x.  1867,  p.  393. 


£66  GENEEAL  EESULTS.  Chap.  XII 

a  species  fertilised  with  pollen  from  a  distinct  genus. 
The  degree  of  sterility  is  much  affected  by  the  condi- 
tions to  which  the  plants  have  been  subjected,*  The 
pollen  from  a  distinct  form  is  strongly  prepotent  over 
that  from  the  same  form,  although  the  former  may 
have  been  placed  on  the  stigma  many  hours  afterwards. 
The  offspring  from  a  union  between  plants  of  the  same 
form  are  more  or  less  sterile,  like  hybrids,  and  have 
their  pollen  in  a  more  or  less  aborted  condition  ;  and 
some  of  the  seedlings  are  as  barren  and  as  dwarfed  as 
the  most  barren  hybrid.  They  also  resemble  hybrids  in 
several  other  respects,  which  need  not  here  be  specified 
in  detail, — such  as  their  sterility  not  corresponding 
in  degree  with  that  of  the  parent  plants, — the  unequal 
sterility  of  the  latter,  when  reciprocally  united, — 
and  the  varying  sterility  of  the  seedlings  raised  from 
the  same  seed-capsule. 

We  thus  have  two  grand  classes  of  cases  giving  results 
which  correspond  in  the  most  striking  manner  with 
those  which  follow  from  the  crossing  of  so-called  true 
and  distinct  species.  With  respect  to  the  difference 
between  seedlings  raised  from  cross  and  self  fertilised 
flowers,  there  is  good  evidence  that  this  depends  alto- 
gether on  whether  the  sexual  elements  of  the  parents 
have  been  sufficiently  differentiated,  by  exposure  to 
different  condition  or  by  spontaneous  variation.  It 
is  probable  that  nearly  the  same  conclusion  may  be 
extended  to  heterostyled  plants ;  but  this  is  not  the 
proper  place  for  discussing  the  origin  of  the  long- 
styled,  short-styled  and  mid-styled  forms,  which  all 
belong  to  the  same  species  as  certainly  as  do  the  two 
sexes  of  the  same  species.  We  have  therefore  no  right 
to  maintain  that   the   sterility  of  species  when  first 


Journal  Linn.  Soc.  Bot.'  vol.  viii.  1864,  p.  180. 


Chap.  XII.  GENERAL  RESULTS.  467 

crossed  and  of  their  hybrid  offspring,  is  determined  by 
some  cause  fundamentally  different  from  that  which 
determines  the  sterility  of  the  individuals  both  of 
ordinary  and  of  heterostyled  plants  when  united  in 
various  ways.  Nevertheless,  I  am  aware  that  it  will 
take  many  years  to  remove  this  prejudice. 

There  is  hardly  anything  more  wonderful  in  nature 
than  the  sensitiveness  of  the  sexual  elements  to  external 
influences,  and  the  delicacy  of  their  affinities.  We  see 
this  in  slight  changes  in  the  conditions  of  life  being 
favourable  to  the  fertility  and  vigour  of  the  parents, 
while  certain  other  and  not  great  changes  cause  them 
to  be  quite  sterile  without  any  apparent  injury  to  their 
health.  We  see  how  sensitive  the  sexual  elements  of 
those  plants  must  be,  which  are  completely  sterile  with 
their  own  pollen,  but  are  fertile  with  that  of  any  other 
individual  of  the  same  species.  Such  plants  become 
either  more  or  less  self-sterile  if  subjected  to  changed 
conditions,  although  the  change  may  be  far  from  great. 
The  ovules  of  a  heterostyled  trimorphic  plant  are 
affected  very  differently  by  pollen  from  the  three  sets 
of  stamens  belonging  to  the  same  species.  With 
ordinary  plants  the  pollen  of  another  variety  or  merely 
of  another  individual  of  the  same  varietyis  often  strongly 
prepotent  over  its  own  pollen,  when  both  are  placed 
at  the  same  time  on  the  same  stigma.  In  those  great 
families  of  plants  containing  many  thousand  allied 
species,  the  stigma  of  each  distinguishes  with  unerr- 
ing certainty  its  own  pollen  from  that  of  every 
other  species. 

There  can  be  no  doubt  that  the  sterility  of  dis- 
tinct species  when  first  crossed,  and  of  their  hybrid 
offspring,  depends  exclusively  on  the  nature  or  affi- 
nities of  their  sexual  elements.  We  see  this  in  the 
want  of  any  close  correspondence  between  the  degree 


468  GENERAL  RESULTS.  Chap.  XII. 

of  sterility  and  the  amount  of  external  difference  in  the 
species  which  are  crossed ;  and  still  more  clearly  in  the 
wide  difference  in  the  results  of  crossing  reciprocally 
the  same  two  species ; — that  is,  when  species  A  is 
crossed  with  pollen  from  B,  and  then  B  is  crossed  with 
pollen  from  A.  Bearing  in  mind  what  has  just  been 
said  on  the  extreme  sensitiveness  and  delicate  affinities 
of  the  reproductive  system,  why  should  we  feel  any 
surprise  at  the  sexual  elements  of  those  forms,  which 
we  call  species,  having  been  differentiated  in  such  a 
manner  that  they  are  incapable  or  only  feebly  capable 
of  acting  on  one  another  ?  We  know  that  species  have 
generally  lived  under  the  same  conditions,  and  have 
retained  their  own  proper  characters,  for  a  much  longer 
period  than  varieties.  Long-continued  domestication 
eliminates,  as  I  have  shown  in  my  'Variation  under 
Domestication,'  the  mutual  sterility  which  distinct 
species  lately  taken  from  a  state  of  nature  almost  always 
exhibit  when  intercrossed ;  and  we  can  thus  understand 
the  fact  that  the  most  different  domestic  races  of  animals 
are  not  mutually  sterile.  But  whether  this  holds  good 
with  cultivated  varieties  of  plants  is  not  known,  though 
some  facts  indicate  that  it  does.  The  elimination  of 
sterility  through  long-continued  domestication  may 
probably  be  attributed  to  the  varying  conditions  to 
which  our  domestic  animals  have  been  subjected ;  and 
no  doubt  it  is  owing  to  this  same  cause  that  they  with- 
stand great  and  sudden  changes  in  their  conditions  of 
life  with  far  less  loss  of  fertility  than  do  natural  species. 
From  these  several  considerations  it  appears  probable 
that  the  difference  in  the  affinities  of  the  sexual 
elements  of  distinct  species,  on  which  their  mutual 
incapacity  for  breeding  together  depends,  is  caused  by 
their  having  been  habituated  for  a  very  long  period 
each  to  its  own  conditions,  and  to  the  sexual  elements 


Chap.  XII  GENEEAL   EESULTS.  469 

having  thus  acquired  firmly  fixed  affinities.  However 
this  may  be,  with  the  two  great  classes  of  cases  before 
us,  namely,  those  relating  to  the  self-fertilisation  and 
cross-fertilisation  of  the  individuals  of  the  same  species, 
and  those  relating  to  the  illegitimate  and  legitimate 
unions  of  heterostyled  plants,  it  is  quite  unjustifiable  to 
assume  that  the  sterility  of  species  when  first  crossed 
and  of  their  hybrid  offspring,  indicates  that  they 
differ  in  some  fundamental  manner  from  the  varieties 
or  individuals  of  the  same  species. 


INDEX. 


A. 

Abutilon  darwiniij  self- sterile  in 
Brazil,  333, 358  ;  moderately  self- 
fertile  in  England,  344 ;  fertilised 
by  birds,  37 1 

Acacia  sph<xrocephala,  404 

Acanthacese,  96 

Aconitum  napellus,  428 

Adlumia  cirrhosa,  366 

Adonis  aestivalis,  128 ;  measure- 
ments, 128;  relative  heights  of 
crossed  und  self-fertilised  plants, 
277 ;  self-fertile,  365 

Ajuga  reptans,  368 

Allium  cepa  (blood-red  var.),  369 

Anagallis  collina  (var.  grandijlora), 
217,  267;  measurements,  218; 
seeds,  316,  323,  325 

Anderson,  J.,  on  tbc  Calceolaria,  87 ; 
removing  the  corollas,  420 

Anemone,  394 

Aneinophilous  plants,  400;  often 
diclinous,  408 

Antirrhinum  majus  (red  var.),  363 ; 
perforated  corolla,  429 

( white  var.),  363 

(peloric  var.),  363 

Apium  petroselinum,  172 ;  result  of 
expeiiniems,  277 

Argemone  ochroleuca,  366 

Aristotle  on  bees  fi  equenting  flowers 
of  the  suae  species,  415 

Aristolochia,  417 

Arum  maculatum,  417 

B. 

Bailey,  Mr.,  perforation  of  corolla, 
427 

21 


Bartonia  aurea,  170  ;  measurements, 
170,  171 ;  result  of  experiments, 
277 

Bartsia  odontites,  3^9 

Beal,  W.  J.,  sterility  of  Kalmia 
latifolia,  359  ;  on  nectar  in  ltibes 
aureum,  432 

Bean,  the  common,  4S2 

Bees  distinguish  colours,  373;  fre- 
quent the  flowers  of  the  same 
species,  4 1 5,  420 ;  guided  by 
coloured  corolla,  420;  powers  of 
vision  and  discrimination,  422 ; 
memory,  423;  unatti  acted  by 
od'Ur  of  certain  flowers,  423; 
industry,  424;  profit  by  the  co- 
rolla perforated  by  humble-bees, 
427  ;  skill  in  working,  428;  habit, 
431 ;  foresight,  433. 

,   humble,    recognise    varieties 

as  of  one  species,  416 ;  colour 
not  the  sole  guide,  421;  rate  of 
flying,  424 ;  number  of  flowers 
visited,  425;  corolla  perforated 
by,  42o,  433;  skill  and  judgment, 
429 

Belt,  Mr.,  the  hairs  of  Digitalis 
purpurea,  82 ;  Fhaseolus  multi- 
florus,  151 ;  not  visited  by  bees 
in  Nicaragua,  3U0 ;  humming- 
birds carrying  pollen,  371 ;  se- 
cretion of  nectar,  403  ;  in  Acacia 
sphxrocephalus  and  passion- 
flower, 404 ;  perforation  of  corolla, 
430. 

Bennett,  A.  W.,  on  Viola  tricolor, 
123;  structure  of  Impatiensfulva, 
367;  plants  flowering  in  winter, 
3S4 ;  bees  frequenting  flowers  of 
same  species,  41C 


472 


INDEX. 


Ben thorn,  on  protection  of  the 
stigma  in  Synaphea,  412 

Beta  vulgaris,  228  ;  measurements, 
229,  230 ;  crossed  not  exceeded 
by  self-fertilised,  289,  367;  pre- 
potency <<f  other  pollen,  397 

Bignonia,  363 

Bird*,  means  of  fertilisation,  371 

Blaekley,  Mr.,  ou  anthers  of  rye, 
376  ;  pollen  carried  by  wind,  ex- 
perim.  nts  with  a  kite,  406 

Boraginacete,  1>5 

Borayo  officinalis,  1S5,  276;  mea- 
surements, 186;  early  flowering 
of  civsscd,  293;  seeds,  323;  par- 
tially self-sterile,  362 

Bracken  ridge,  Mr.,  organism  of  ani- 
mals affected  by  temperature  and 
fuod,  446;  different  effect  of 
ch  .nged  conditions,  455 

Brassica  oleracea,  96 ;  measure- 
ments, 100;  weight,  101,  102; 
remarks  on  experiments,  262 ; 
superiority  of  crossed,  288  :  period 
of  flowering,  292 ;  seeds,  322 ; 
self-fertile,  365 

napus,  393 

rapa,  393 

Brisout,  M.,  insects  frequenting 
flowers  of  same  species,  419 

Broom,  163 

Brugmansia,  371 ;  humming-birds 
boring  the  flower,  432 

Bulrush,  weight  of  pollen  produced 
by  one  plant,  405 

Bundy,  Mr.,  Itibes  perforated  by 
bees,  432 

Butschli,  O.,  sexual  relations,  409 


C. 


Cabbage,  98 ;  affected  by  pollen  of 
purple  bastard,  378:  prepotency 
of  other  pollen,  393,  397 

,  Ragged  Jack,  395 

Calceolaria,  87,  369 

Galluna  vulgaris,  421 

Campanula  carpathica,  174,  364 

Ctmpanulaceze,  174 

Candolle;    A.  do,  on  ascending  a 


mountain  the  flowers  of  the  same 
species  disappear  abruptly,  3S9 

Canna  ivarscewiczi,  230 ;  Jesuit  of 
crossed  and  self-fertilised,  278 ; 
period  of  flowering,  294  ;  seeels, 
323,  325 ;  highly  self-fertile,  369 

Cannaceee,  230 

Carduus  arctioides,  402 

Carnation,  132 

Carfiere,  relative  period  of  the  ma- 
turity of  the  sexual  elements  on 
same  flower,  441 

Caryopliyllacese,  1 30 

Caspary,  Professor,  on  Corydalit 
cava,  33 1 ;  Nymphmaceie,  358; 
Euryale  ferox,  365 

Cecropia,  food-bodies  of,  404 

Centradenia  jloribunda,  364 

Cereals,  grains  of,  354 

Cheeseman,  Mr.,  on  Orchids  in  New 
Zealand,  390 

Chenopodiacex,  228 

Cineraria,  335 

Clarkia  elegans,  1 69 ;  measurements, 
170 ;  early  flowering  of  self-fer- 
tilised, 294,  29o  ;  seeds,  316 

Cleistogene  flowers,  90 

Coe,  Mr.,  cresting  Phaseolus  vul- 
garis, 153 

Colgate,  B.,  red  clover  never  sucked 
by  hive-bees  in  New  Zealand, 
361 

Colour,  uniform,  of  flowers  on  plants 
self  fertilised  and  grown  under 
similar  conditions  for  several  gene- 
rations, 306,  307 

Colours  of  flowers  attractive  to  in- 
sects, 372 ;  not  the  sole  guide  to 
bees,  421 

Composites,  173 

Coniferie,  401 

Convolvulus  major,  28 

■ tricolor,  55 

Corolla,  removal  of,  420  ;  perforation 
by  be^s,  425 

Coronilla,  405 

Corydalis  cava,  331,  358 

halleri,  331 

intermedia,  331 

lutea,  359 

ochroleuca,  359 


INDEX. 


473 


COEYDALIS. 

Corydalis  solida,  358 

Corylus  avellana,  390 

Cowslip,  219 

Orinum,  395 

Crossed  plants,  greater  constitu- 
tional vigour  of.  285 

Cross-fertilisation,  370 :  see  Fertilisa- 
tion. 

Crossing  flowers  on  same  plant, 
effects  of,  297 

Cruciferse,  98 

Criiger,  Dr.,  spcretion  of  sweet 
fluid  in  Marcgraviacese,  105 

Cuphea  purpurea,  323,  362 

Cycadise,  401 

Cyclamen  persicum,  215;  measure- 
ments, 216;  early  flowering  of 
ciossed,  '^93;  seeds,  317,  323; 
self-sterile,  362 

repandum,  215 

Cytisus  laburnum,  362 


Dandelion,  number  of  pollen  grains, 
376 

Darwin,  C,  self-fertilisation  in 
Pisum  sativum,  161 ;  sexual  affini- 
ties, 209  ;  on  Primula,  219 ;  bud 
variation,  298 ;  constitutional 
vigour  from  cross  parentage  in 
common  -  pea,  305 ;  hybrids  of 
Gladiolus  and  Cistus,  306  ;  Pha- 
seolus muliiflorus,  360;  nectar 
in  orchids,  405 ;  on  cross-ferti- 
lisation, 438,  439,  457;  inheri- 
tance of  acquired  modifications, 
446 ;  change  in  the  conditions  of 
life  beneficial  to  plants  and 
animals,  454 

* ,  F.,    structure     of   Phaseolus 

multijiorus,  150  :  Pteris  aquilina, 
404 ;  perforation  of  Lathyrus 
sylvestris,  420 

,  G.,   on  marriages   with  first 

cousins,  460 

Decaitne  on  Delphinium  consolida, 
129 

De  Candolle,  nectar  as  an  esoretion, 
402 


Delphinium  consolida,  129;  mea- 
surements 130  ;  seeds,  322  ;  par- 
tially sterile,  358;  corolla  re- 
moved, 420 

Delpino,  Professor,  Viola  tricolor, 
123;  Phaseolus  multijiorus,  150; 
intercrossing  of  sweet-pea,  156; 
Lobelia  ramosa,  176 ;  structure 
of  the  Cannacese,  230;  wind  and 
water  carrying  pollen,  371  ; 
Junlans  regia,  390 ;  anemophi- 
lous  plants,  400;  fertilisation  of 
Plantago,  401 ;  excretion  of 
nectar,  402,  405;  secretion  of 
nectar  to  defend  the  plant,  403, 
404 ;  auemophilous  and  entomo- 
philous  plants,  408 ;  dioecious 
plants,  414 

D(.nny,  Pelargonium  zonale,  142 

Diagram  showing  mean  height  of 
Jpomcea  purpurea,  53 

Dianthus  caryophyllus,  132 ;  crossed 
and  self-fertilised,  133-136  ;  mea- 
surements, 135-138;  cross  with 
fresh  stock,  136 ;  weight  of  seed, 
139;  colour  of  flowers,  139;  re- 
marks on  experiments,  263,  274  ; 
early  flowering  of  crossed,  292 ; 
uniform  colour  of  self-fertilised, 
309;  seeds,  316,  319,  323,  325; 
few  capsules,  360 

Dickie,  Dr.,  self-fertilisation  in 
Cannacese,  230 

Dictamnus  fraxinella,  413 

Digitalis  purpurea,  81 ;  measure- 
ments, 84-87;  effects  of  inter- 
crossing, 85,  299  ;  superiority  of 
crossed,  288,  447 ;  self-sterile, 
363 

Dipsacex,  172 

Dobbs,  bees  frequenting  flowers  of 
same  species,  416 

Dodel,  Dr.  A.,  sexual  reproduction, 
409 

Duliamel  on  Eaphanus  sativus, 
393 

Dumil,  nectar  as  an  excretion, 
402 

Dyer,  Mr.,  on  Lobelia  ramosa,  176 ; 
on  Cineraria,  335 


474 


INDEX. 


E. 


Eariey,  "W.,  self-fertilisation  of 
Lathyrus  odoratus,  153 

Eaton,  Kev.  A.  E.,  on  Pringlea,  408 

Engelmann,  development  of  sexual 
forms,  409 

Engler,  Dr.,  on  dichogamous  Saxi- 
fraga,  440 

Entomophilous  plants,  408 

Epipactis  latifolia,  attractive  only 
to  wasps,  375,  423 

Erica  tetralix,  421  ;  perforated 
corolla,  426,  434 

Erythrina,  360 

Eschscholtzia  californica,  1 09 ; 
measurements,  110  ;  plants  raised 
from  Brazilian  seed,  111 ;  weight, 
113;  seeds,  115,  116,  315,  319, 
322  ;  experiments  on,  263,  275 ; 
superiority  of  self-fertilised  over 
crossed,  290;  early  flowering, 
292,  294;  artificially  self-ferti- 
lised, 3  i2  ;  pollen  from  other 
flowers  more  effective,  340 ;  self- 
sterile  in  Brazil,  343,  358 

Euphrasia  officinalis,  368 

Euryale  amazonica,  358 

ferox,  365 


Fahricius  on  Aristolochia,  417 

Fagopyrum  esculentum,  228 ;  early 
flowering  of  crossed  plant,  293 

Faivre,  Professor,  self-fertilisation 
of  Cannacex,  230 

Farrer,  T.  H.,  papilionaceous 
flowers,  5  ;  Lupinus  luteus,  147  ; 
Fhaseolus  multiflorus,  150,  431 ; 
Pisum  'sativum,  160 ;  cross-fer- 
tilisation of  Lobelia  ramosa,  176  ; 
on  Coronilla,  405 

Fermond,  M..  Fhaseolus  multi- 
florus, 151 ;  P.  ooccineus  hybridus, 
151 

Fertilisation,  means  of,  356  ;  plants 
steiile,  or  partially  so  without 
insect-aid,  357-364 ;   plants  fer- 


tile without  insect-aid,  365-369 ; 
means  of  cross-fertilisation,  370 ; 
humming-birds,  371;  Australian 
flowers  fertilised  by  honey- 
sucking  birds,  371 ;  in  New  Zea- 
land by  the  Anthornis  melanura, 
371 ;  attraction  of  bright  colours, 
372 ;  of  odours,  374 ;  flowers 
adapted  to  certain  kinds  of  insects, 
375 ;  large  amount  of  pollen- 
grains,  376,  377 ;  transport  of 
pollen  by  insects,  377-379 ;  struc- 
ture and  conspicuousness  of 
flowers,  381 ;  pollen  from  a  dis- 
tinct plant,  388 ;  prepotent 
pollen,  393-400 

Fertility,  heights  and  weights,  re- 
lative, of  plants  crossed  by  a 
fresh  stock,  self-fertilised,  or 
intercrossed  (Table  C),  245- 
252 

Fertility  of  plants  as  influenced  by 
cross  and  self-fertilisation  (Table 
D),  312 ;  relative,  of  crossed  and 
self-fertilised  parents  (Table  E), 
314-319;  innate,  from  a  cross 
with  fresh  stock  (Table  F),  319  ; 
relative,  of  flowers  crossed  with 
pollen  from  a  distinct  plant  and 
their  own  pollen  (Table  G),  320  ; 
of  crossed  and  self-fertilised 
flowers,  324,  325 

Flowering,  period  of,  superiority  of 
crossed  over  self-fertilised,  291- 
297    . 

Flowers,  white,  larger  proportion 
smelling  sweetly,  374 ;  structure 
and  conspicuousness  of,  381 ;  con- 
spicuous and  inconspicuous,  385  ; 
papilionaceous,  o85 ;  fertilised 
with  pollen  from  a  distinct  plant,. 
388 

Forsythia  viridissirna,  341 

Foxglove,  81 

Franklaud,  Dr.,  chemical  affinitv, 
456 

Fraxinus  ornus,  402 

Fumaria  capreolata,  366 

■'■  -  ■  officinalis,  366 


INDEX. 


475 


G. 

Galium  aparine,  369 

Gallesio,  spontaneous  crossing  of 
oranges,  394 

Gal  ton,  Mr.,  Limnanthes  douglasii, 
146 ;  report  on  the  tables  of 
measurements,  16-19,  146,  234 ; 
self-fertilised  plants,  290,  291 ; 
superior  vigour  of  crossed  seed- 
lings in  Lathyrus  odoratus,  353, 
355 

Gartner,  excess  of  pollen  injurious, 
24 ;  plants  fertilising  one  another 
at  a  considerable  distance,  152 ; 
Lobeliafulgens,  179,  330 ;  sterility 
of  Verbascum  nigrum,  330  ;  number 
of  pollen-giains  to  fertilise  Geum 
urbanum,  377  ;  experiments  with 
pollen,  379 

Gentry,  Mr.,  perforation  of  corolla, 
427 

Geraniaceie,  142 

Geranium  phieum,  420 

Gerard  ia  pedicularia,  427 

Germination,  period  of,  and  relative 
weight  of  seeds  from  crossed  and 
selt'-tertilised  flowers,  352-355 

Gesneria  pendulina,  92  ;  measure- 
ments, 92 ;  seeds,  322 

Grsneriaceas,  92 

Geum  urbanum,  number  of  pullen- 
g rains  for  fertilisation,  377 

Glaucium  luteum,  366 

Godron,  intercrossing  of  carrot,  172  ; 
Primula  grandiflora  affected  by 
pollen  of  P.  officinalis,  378 ;  tulips, 
394 

Gould,  humming-birds  frequenting 
Impatiens,  371 

Graminacese,  233,  440 

Grant,  Mr.,  bees  of  different  hives 
visiting  different  kinds  of  flowers, 
423 

Gray,  Asa,  sexual  relations  of  trees 
in  United  States,  412  ;  on  sexual 
reproduction,  439 


Hallet,  Major,  on  selection  of  grains 
of  cereals,  354 


HOFFMANN. 

Hassall,  Mr.,  number  of  pollen- 
grains  in  Pseony  and  Dandelion, 
376 ;  weight  of  pollen  produced 
by  one  plant  of  Bulrush,  405 

Heartsease,  123 

Hedychium,  364 

Hedysarum  onobrychis,  361 

Heights,  relative,  of  crossed  and 
self- fertilised  plants  (^Table  A), 
240-243 

Heights,  weights,  and  fertility, 
summary,  238-284 

Henschel's  experiments  with  pollen, 
379 

Henslow,  Eev.  G.,  cross  fertilisa- 
tion in  Sarothamnus  scoparius, 
164 

Herbert  on  cross-fertilisation,  7; 
pollen  brought  fiom  distant 
plants,  37S ;  spontaneous  crossing 
of  rhododendrons,  394 

Hero,  descendant*  of  the  plant,  47- 
51,  258;  its  self-fertilisation,  349 

Heterocentron  mexicavum,  361 

Hibiscus  africanus,  140 ;  measure- 
ments, 140 ;  result  of  experiments, 
277 ;  early  flowering  ot  crossed 
plant,  292, 296  ;  number  of  pollen- 
grains  for  fertilisation,  377 

Hildebrand  on  pollen,  of  Digitalis 
purpurea,  82  ;  Thunbergia  alata, 
96 ;  experiments  on  Eschscholtzia 
calif ornica .  110  ;  Vinla  tricolor, 
123 ;  Lobelia  ramosa,  176  ;  Fago- 
pyrum  esculentum,  228 ;  self-fertili- 
sation of  Zea  mays,  233  ;  Corydalis 
cava,  33 1 ;  Bypecoum  grandi- 
florum,  331,  35.' ;  and  H.  pro- 
cumbens,  331, 366; ;  sterility  of  Esch- 
scholtzia, 332 ;  experiments  on  self- 
fertilisation,  340 ;  Corydalis  lutea. 
359 ;  spontaneously  self-fertilised 
flowers,  366;  various  mechanical 
structure  to  check  self-fertilisa- 
tion, 382  ;  early  separation  of  tiie 
sex'js,  400;  on  Aristolochia,  417; 
fertilisation  of  the  Graminese,  440 ; 
wide  dissemination  of  seeds,  450 

Hoffmann,  Prof.  H.,  self-fertilised 
cap&ules  of  Papacer  somniferum, 
108,  366;  Adonis  aativalis,  129, 


476 


INDEX. 


IIOXEY  DEW. 

365;  spontaneous  variability  of 
1'haseolus  multiflorus,  151 ;  self- 
fertilisation  of  kidney-bean,  152; 
Fapaver  alpinum,  331 ;  sterility 
of  Corydalis  solida,  358;  Linum 
usitatissimum,  366 

Honey-dew,  402 

Hooker.  Dr.,  Euryale  ferox  and 
Victoria  regia,  each  producing 
several  flowers  at  once,  365;  on 
sexual  relation  of  trees  in  New 
Zealand,  411 

Horse-chestnut,  399 

Humble-bees,  416 :  see  Bees 

Humboldt,  on  the  grains  of  cereals, 
354 

Humming-birds  a  means  of  cross- 
fertilisation,  371 

Hyacinth,  :i94 

Hybrid  plants,  tendency  to  revert  to 
their  parent  forms,  379 

Hypecoum  grandiflorum,  331,  359 

procumbens,  331,  366 


Iberis  umbellata  (var.  kermesiana'), 
103  ;     measurement,      104-106 
cross    by     fresh     stocks,     105 
remarks    on    experiments,    262 
Blip,  riority  of  crossed  over  self- 
fertilised  seedlings,    289 ;    early 
flo-vering,  292;  number  of  seeds, 
315;     highly    self-fertile,     365; 
prepotency  of  other  pollen,  392 

amara,  305 

Impatiens  frequented  by  humming- 
birds, 371 

■ barbigera,  366 

fulva,  341,  367 

noli-me-tangere,  367 

pallida,  341 

Inheritance,  force  of,  in  plants,  305 

Insects,  means  of  cross-tVrtilisation, 
371 ;  attracted  by  bright  colours, 
372 ;  by  odours,  374 ;  by  con- 
epicuous  flowers,  383;  dark 
6treaks  and  marks  as  guides  for, 
372 ;  flowers  adapted  to  certain 
kinds,  375 


Ipomcea  purpurea,  28;  measure- 
ments, 29-49 ;  flowers  on  same 
plant  crossed,  41-44;  cross  with 
fresh  stock,  45-47 ;  descendants 
of  Hero,  47-51  ;  summary  of 
measurements,  52;  diagram  show- 
ing mean  heights,  53  ;  summary 
of  observations,  53-62  ;  of  experi- 
ments, 257-259;  superiority  of 
crossed,  289 ;  early  fl<  >wering, 
291,  297  ;  effects  of  intercrossing, 
300;  uniform  colour  of  seif-fr-r- 
tib's^d,  308 ;  seeds,  314,  322,  324  ; 
highly  self-fertile,  368 ;  prepo- 
tency of  other  pollen,  397 

Iris,  secretion  of  saccharine  matter 
from  calvx,  402 

Isotoma,  176,  364 


Juglans  regia,  390 


Ealmia  latifolia,  359 

Kerner,  on  protection  of  the  pollen, 
376;  on  the  single  daily  flower 
of  Villarsia  pamassifolia,  390 ; 
pollen  carried  by  wind,  405,  406, 
412 

Kidney-bean,  152 

Kitchener,  Mr.,  on  the  action  of  the 
stigma,  6t;  on  Viola  tricolor,  123 

Knight,  A.,  on  the  sexual  intercourse 
of  plants,  7 ;  crossing  varieties  of 
peas,  163 ;  sexual  reproduction, 
439 

Kohl-rabi,  prepotency  of  pollen, 
393 

Kolreuter  on  cross-fertilisation,  7; 
number  of  pollen-grains  necessary 
for  fertilisation,  24 ;  sexual  affini- 
ties of  Nicotiana,  210  ;  Verbascum 
phaeniceum,  330;  experiments 
with  pollen  of  Hibiscus  vesi- 
carius,  377 

Kuhn  adopts  the  term  cleistogene, 
90 

Kurr,  on  excretion  of  nectar,  402' 
removal  of  corolla,  420 


INDEX. 


477 


Lalriatm,  93 

Lactuca  safiva,  17°>,  369;  mensnre- 
me  it,  174;  prepotency  of  other 
poll,n,  397 

Lctmium  album,  3S9,  416 

jmrpurenm.  416 

Lathy  rus  odoratus,  151-160;  mea- 
surements, 157-160;  remarks 
on  oxpeiiments,  265:  period  of 
flowering.  295 ;  cross-fertilisation, 
304 ;  seeds,  316,  325 ;  self-fertile, 
367 

grand iflorus,  155,  360 

nissolia.  367 

syloestris,  perforation  of  corolla, 

429 

Lawes  and  Gilbert,  Messrs.,  con- 
sumption of  inorganic  matter  by 
plants,  4l8 

Laxton,  Mr.,  crossing  varieties  of 
peas,  163,  305 

Lecop  Cyclamen  repandum,  215  ;  on 
Fumar.'acex,  359 ;  animal  piauts 
rarely  dioecious,  413 

Leersia  oryzoides,  350 

Leguminosx,  147  ;  summary  on  the, 

ies 

Lei,irhton,  Rev.  W.  A.,  on  Phaseolus 
multiflorus,  151 ;  Acacia  magnified, 
405 

Leptosiphon  androsaceus,  368 

Leschenaultia  formosa,  364 

Lettuce,  173 

Lilium  auratum,  341 

Limnanthesdouglasii,  145 ;  measure- 
ments, 146;  e.irly  flowering  of 
crossed,  293;  seeds,  316,  323; 
highly  self-fertile,  367;  prepo- 
tency of  other  pollen,  3S7 

Linaria  vulgaris,  9,  88  ;  seeds,  322 ; 
self-sterile,  363 

ajmbalaria,  384,  422 

Lindley  on  Fumariaceie,  359 

Link,  hypopetalous  nectary  in 
Chironia  decussata,  403 

Linam  grandiflorum,  343 

■ usitatissimum,  366 

Loasacex,  170 


Lobelia  erinus,  176;  secretion  of 
nectar  in  suns  .in  ,  403;  experi- 
m  nts  with  bees,  420 

Lobelia ful gens,  179  ;  measurements, 
1  .SO— 18^i :  summary  of  experi- 
ments. 274;  early  flowering  of 
self-fertilise- 1,  291,  2.)4,  295; 
seed  ■,  323  ;  sterile  unless  visited 
by  humble-bees,  364 

ramosa,  176;    measurements, 

177,  178;  early  flowering  of 
crossed,  293,  295;  seeds,  "325; 
self-sterile,  3J4 

tenuior,  176 

Loise!eur-Deslon»ch,\mp,  on  the 
grains  of  cereals,  354 

Lotus  corniculatus,  361 

Lubbock,  Sir  J.,  cross-fertilisation 
of  Mowers,  6;  on  Viola  tricolor, 
123;  bees  distinguishing  colours, 
373 ;  instinct  of  bees  and  injects 
sucking  nectar.  415 

Lupinus  luteus,  147;  measurements, 
148;  early  flowering  of  self-ferti- 
lised, 294,"  296;  self-fertile,  367; 
prepotency  of  other  pollen,  397 

pilosus,  149  ;  self-fertile,  567 

Lychnis  dioica,  411 


M. 


Macnab,   Mr.,   on    the    shorter    or 

longer  stamens  of  rhododendrons, 

298 
Mahonia  aquifolium,  395 

repens,  895 

Malcacem,  140 

Marcgraviacex,  404 

Masters,   Mr.,  cross-fertilisation  in 

Pisum  sativum,    161;    cabbages 

affected  by  pollen  at  a  distance, 

378 
,  Dr.  Maxwell,  on  honey-dew, 

402 
Measurements,    summary   of,  241  ; 

Table    A,    240-243;    Table    B, 

244  ;  Table  C,  245-252 
Medicago  hipuiina,  368 
Meehan,    Mr.,    fertilising;   Pelunia 

violacea  by  night  moth,  1S8 


478 


INDEX. 


MELASTOMACEiE. 

Melastomacex,  298 

Melilotus  officinalis,  360 

Mercurialis  annua,  413 

Miller,  Professor,  on  chemical  affi- 
nity, 456 

Mimulus  luteus,  effects  of  crossing, 
10;     crossed    and     self-fertilised 
plants,  64-70  ;  measurements,  70- 
78  ;  cross  with  adistinct  stock.  72- 
75  ;    intercrossed  on  same  plant. 
75-78  ;  summary  of  observations 
78-81 ;  of  experiments,  259-261 
superiority  of  crossed  plants,  286 
simultaneous  flowering,  294,  296 
effects     of     intercrossing,     301 
uniform  colour  of  self-fertilised 
307;    beeds,  315,  319,  322,  324 
highly  self-fertile,  348,  369 ;  pre- 
potency of  other  pollen,  392,  397 

roseus,  63 

Miner,  Mr.,  red  clover  never  sucked 
by  hive-bees  in  the  United  States, 
361 

Mirobilis,  dwarfed  plants  raised  by 
using  too  few  pollen-grains,  298  ; 
number  of  grains  necessary  for 
fertilisation,  377 

Mitchell,  Dr.,  on  first-cousins  inter- 
marrying, 460 

Monochoetum  ensiferum,  364 

Moure,  Mr.,  on  Cinerarias,  335 

Midler,  Fritz,  on  Posoqueria 
fragrans,  5,  391 ;  experiments  on 
hybrid  Abutilons  and  Bignonias, 
305,  306;  large  number  of 
orchidaceous  genera  sterile  in 
their  native  home,  also  Bignonia 
and  Tabernxmontana  echinata, 
331 ;  sterility  of  Eschscholtzia 
californica,  332,  342 ;  Abutilon 
darwinii,  334;  experiments  in 
self-fertilisation,  340;  selt'-sterile 
plants,  341 ;  incapacity  of  pollen- 
tubes  to  penetrate  the  stigma, 
342  ;  cross-fertilisation  by  means 
of  birds,  371 ;  imperfectly  deve- 
loped male  and  female  Termites, 
3S0 ;  food-bodies  in  Cecropia,  404 

M idler,  Hermann,  fertilisation  of 
flowers  by  insects,  6,  7 ;  on 
Digitalis  purpurea,  82;    Calceo- 


laria, 87  ;  Linaria  vulgarity,  88  ; 
Verbascum  nigrum,  89 ;  the 
common  cabbage,  98;  Pavacer 
dubium,  107;  Viola  tricolor,  123, 
124;  structure  of  Delphinium 
coiisoliila,  129;  of  Lupinns  lutea, 
147  ;  flowers  of  Pisum  sativum, 
160,  161;  on  Sarothamnus  scapa- 
rius  not  secreting  nectar,  164  ; 
Apium  petroselinum,  172  ;  Borago 
officinalis,  1S5;  red  clover  visiled 
by  hive-bees  in  Germany,  361 ; 
insects  rarely  visiting  Fumaria 
officinalis,  366 ;  comparison  of 
lowland  and  alpine  species,  375; 
structure  of  plants  adapted  to 
cross  and  self- fertilisation,  380; 
large  conspicuous  flowers  more 
frequently  visited  by  insects  than 
small  inconspicuous  ones,  383; 
Solatium  generally  Unattractive 
to  insects,  387  ;  Lamium  album, 
389 ;  on  anemophilous  plants, 
400  ;  fertilisation  of  Plantago, 
401 ;  secretion  of  nectar,  405 ; 
instinct  of  bees  sucking  nectar, 
415;  bees  frequenting  flowers  of 
the  same  species,  416;  cause  of 
it,  419;  powers  of  vision  and 
discrimination  of  bees,  422 

Midler,  Dr.  H„  hive-bees  occa- 
sionally perforate  the  flower  of 
Erica  tetralix,  427;  calyx  and 
corolla  of  Ehinantlius  alectero- 
lophus  bored  by  Bombus  mastru- 
catus,  432 

Munro,  Mr.,  some  species  of  Onci- 
clium  and  Maxillaria  sterile 
with  own  pollen,  331 

Myrtacex,  412 


N. 


N'ageli  on  odours  attracting  insects, 
374  ;  sexual  relations,  4  09 

Natural  selection,  effect  upon  self- 
sterility  and  self-fertilisation,  345, 
346 

Naudin  on  number  of  pollen-grains 
necessary  for  fertilisation,  24 ; 
Petunia  violaeea,  188 


INDEX. 


479 


Nectar  regarded  as  an  excretion,  402 

Nenwphila  insignis,  182;  measure- 
ments, 1S3-1H5;  early  flowering 
of  crossed  plant,  293 :  effects  of 
cross  and  self-fertilisation,  303; 
seeds.  316,323 

Nepeta  glechoma,  41 6 

Nicotiana  glutinosa,  210 

■ tabacum,  203  ; '  measurements, 

205-208;  cross  with  fresh  stock, 
210;  measurements,  212-215; 
summary  of  experiments,  266,  267, 
279  ;  superiority  of  crossed  plants, 
288-290;  early  flowering,  293- 
295;  see<ls,  323,  325;  experi- 
ments on.  349  ;  self-fertile,  368 

Nolana  prostrata,  186;  measure- 
ments, 187;  crossed  and  self- 
fertilised  plants,  277;  number  of 
capsules  and  seeds,  321,  323  ; 
self-fertile,  368 

Nolanacese,  186 

Nymphxa,  358,  365 


Odours  emitted  by  flowers  attractive 
to  insects,  374 

Ogle,  Dr.,  on  Digitalis  purpurea, 
82  ;  Gesneria,  92  :  Phaseolus  mul- 
tiflorus,  151,  3u'0,  431  ;  perfora- 
tion of  corolla,  426  ;  case  of  the 
Monkshood,  428 

Onagracese,  169 

Onion,  prepotency  of  other  pollen, 
393 

Ononis  minutissima,  167  ;  measure- 
ments, 168 ;  seeds,  323 ;  self- 
fen  ile,  367 

Ophrys  apifera,  350,  369,  439 

—    muscifera,  384,  406 

Oranercs,  spontaneous  crossing,  394 

Orchideee,  364.  369 ;  excretion  of 
saccharine  matter,  402 

Orchis,  fly,  406 

Origanum  vulgare,  94 ;  measuro- 
ninnH  95;  early  flowering  of 
crossed  plant,  292 ;  effects  of 
intercrossing,  301 


PHASEOLUS. 


P. 


Pseony,  number  of  pollen-grains, 
376 

Papaveracefe,  107 

Papaver  alpinum,  331,  358 

argemonoides,  366 

bracteatum,  108 

dubium,  1 07 

orientale,  108 

rhozas,  li)7 

somniferum,  108,  331,  365 

vagum,    107 ;     measurements, 

109  ;  number  of  capsules,  315  ; 
seeds,  358  ;  prepotency  of  other 
pollen,  397 

Papillse  of  the  Viola  tricolor  at- 
tractive to  insects,  124 

Parsley,  172 

Passiflora  alata,  330,  334 

gracilis,   171 ;    measurements, 

171;  crossed  and  self-fertilised, 
276;  seeds,  323;  self  -  fertile, 
365 

Passifloracese,  171,  357 

Pea,  common,  160,  351 

Pelargonium  zonale,  142 ;  measure- 
ment*, 143  ;  <  ffects  of  inter- 
crossing, 301 ;  almost  self-sterile, 
359 

Pentstemon  argutus,  perforated  co- 
rolla, 426,  4  28,  433 

Petunia  violacea,  188 ;  measure- 
ments, 189-203;  weight  of  seed, 
196 ;  cross  with  fresh  stock,  196- 
201 ;  relative  f.  rtility,  201-203  ; 
colour,  203 ;  summary  of  experi- 
ments, 265,  274;  superiority  of 
crossed  over  self-fertilised,  289; 
eailv flowering, 293,  294 ;  uniform 
colour  of  self-fertiliserl,  309 ; 
seeds,  316,  319,  323,  325;  self- 
stenle,  362 

Phalaris  canariensis,  235  ;  measure- 
ments, 236,  237 ;  early  flowering 
of  crossed  2'-i3 

Phaseolus  coccineus,  1-t0 

multiflorus,  150 ;  measurement, 

152;  p.itially  sterile,  168,  360; 
crossed  and  self-fertilised,  276  ; 


180 


INDEX. 


PHASEOLUS. 

early  flowering  of  crossed,  293 ; 
seeds,  316 ;  perforate  1  by  hunible- 
bees,  430 

Fhaxeoltis  vulgaris,  153;  self-fertile, 
1G8,  367 

Pisum  sativum,  160  ;  measurements, 
162;  seld >m  intercross,  160; 
summary  of  experiments,  264, 
278;  self-fertile,  367 

Plants,  crossed,  greater  consti- 
tutional vigour,  285 

Fleroma,  364 

Polemoniacex,  182 

Pollen,  relative  fertility  of  flowers 
crossed  from  a  distinct  plant,  or 
with  their  own,  320 ;  difference 
of  results  in  Nolana  prostrata,  321, 
323 ;  crossed  and  self-fertilised 
plants,  again  crossed  from  a 
distinct  plant  and  their  own  pol- 
len, 324  ;  sterile  with  their  own, 
330-338  ;  seuii-self-sterile,  338- 
340 ;  loss  of,  376 ;  number  of 
grains  in  Dandelion,  Pseony,  and 
Wistaria  sinensis,  376 ;  number 
necessary  for  fertilisation,  377 ; 
transported  from  flower  to  flower, 
377  ;  prepotency,  391-400  ;  abori- 
ginally the  sole  attraction  to  in- 
sects, 402  ;  quantity  produced  by 
anemophilous  plants,  405 

Polvanthus.  prepotency  over  cow- 
slip, 396 

Polygoneie,  228 

Posoqneria  fiagrans,  5,  391 

Potato,  387 

Poterium  sanguisorba,  407 

Potts,  heads  of  Anthornis  melanura 
covered  with  pollen,  371 

Primrose,  Chinese,  225 

Primula  elatior,  422,  427 

■ grandijlora,  378 

mollis,  368 

officinalis,  378 

: scotica ,  362 

—  sinensis,  225,  279 ;  measure- 
ments, 227 ;  early  flowering  of 
crossed,  293,  296 

— —  veris  (var.  officinalis'),  219 ; 
measurements,  221 ;  result  of  ex- 
periments, 267,  268 ;  early  flower- 


ing of  crossed,  293;  seeds,  317; 
self-fertility,  351 ;  prepotency  of 
dark  red  polyanthus,  396 

Primulacex,  215 

Pringlea,  408 

Proteacex  of  Australia,  412 

Prunus  avium,  403 

laurocerasus,  401 

Pteris  aquilina,  404 


E. 

Radish,  393 

Ranunculaceie,  128 

Ranunculus  acris,  365 

Raphanus  sativus,  365,  393 

Reinke,  nectar-secieting  glands  of 
Prunus  avium,  403 

Eeseda  lutea,  117;  measurements, 
118,  119;  result  of  experiments, 
339;  self  fertile,  365 

odorata,  119;   measurements, 

120-123 ;  self-fertilise  J  scarcely  ex- 
ceeded by  crossed,  289 ;  seeds,  316; 
want  of  correspondence  between 
seeds  and  vigour  of  offspring, 
328;  result  of  experiments,  336; 
sterile  and  self-fertile,  358,  365 

Resedaceas,  117 

Rheum  rhaponticum,  401 

Rhexia  glandulosa,  364 

Rhododendron,  spontaneous  cross- 
ing, 394 

Rhododendron  azaloides,  432 

Rhubarb.  391,  401 

Ribes  aureum,  432 

Riley,  Mr.,  pollen  carried  by  wind, 
405;  Yucca  moth,  418 

Rodders,  Mr.,  secretion  of  nectar  in 
Vandla,  408 

Rye,  experiment  on  pollen  cf,  376 


S. 

Salvia  coccmea,  93 ;  measurements, 
93 ;  early  flowering  of  crossed, 
292;  seeds,  315,  322;  partially 
self-sterile,  363 

glutinosa,  427 


INDEX. 


481 


Salvia  graliami,  420,  42S,  433 

tenon,  302 

Sarothamnus  scoparius,  163;  mea- 
sure! 1 1 1- 1 its,  l-i 55-1 67  ;  superiority 
of  crossed  seedli.igs,  28.i,  289 ; 
seed s  323:  self-sterile,  3ti0 

Seabiosa  atro-purpurea,  172;  mea- 
surements, 172,  173 

Scarh  t-runner,  150 

Scott,  J.,  Papaver  somniferum,  108  ; 
steril.ty  of  Verbascum,  330 ;  On- 
cidium  and  Maxillaria,  331  ;  on 
Primula  scoti  a  and  Cortusa  mat- 
thioli,  362 

Scrophulariacete,  63 

Self-feitile  varieties,  appearance  of, 
347-351 

Self-fertilisation,  mechanical  struc- 
ture to  check,  382 

Self-sterile  plants,  f.29-347;  wide 
dlstribut  on  throughout  the 
vegetable  kingdom,  341  ;  differ- 
ence in  plants,  342 ;  cause  of 
self-sterility,  343 ;  affected  by 
changed  conditions,  344-346 ; 
necessity  of  differentiation  in  the 
sexual  elements.  317 

Senecio  emeritus,  335,  364 

heritieri,  3  >5 

maderensis,  335 

populifoius,  335 

tussilaginis,  3:->5 

Sliaipe,  Mes>rs.,  precautions  against 
intei  crossing,  395 

Snow-Hake,  176 

Solanaceie,  1S8 

Solanum  tuberosum,  362,  387 

Specularia  per/oliata,  174 

speculum,  174;  measurements, 

175,  176;  crossed  and  self-ferti- 
lised. 216;  early  flowering  of 
crossed,  293 ;  seeds,  323 ;  self- 
fertile,  369 

Spencer,  Herbert,  chemical  affinity, 
457 

Spiranthes  autumnalis,  391,  421 

Spreiiirel,  C.  K,  fei filiation  of 
flowers  by  insects,  5,  6  ;  Viola 
tricolor,  123 ;  colours  in  flowers 
attract  and  guide  insects,  372, 
373 ;  on  Aristolochia,  ill ;  Aconi- 


tum  napellus,  428  ;  importance  of 

insects  in  fertilising  flowers,  455 
Stachi/s  coccinea.  426,  428,  433 
Stellaria  media,  367 
Strachey,  General,  perforated  flowers 

in  ttie  Hima  aya,  434 
Strawberry,  3.*4 
Strelitzia  fertilised  by  the  Nectarini- 

deie,  371 
Structure  of  plants  adapted  to  cross 

and  self  fertilisation,  380 
Swale,  Mr.,  garden  lupine  not  visited 

by  bees  in  New  Zealand,  150 
Sweet-pta,  153 


Tabernannontana  ecliinata.  331,  362 

Table.-  of  Hi'  asuretnents  of  heighrs, 
weights,  and  fertility  of  plants, 
240-270 

Termites,  imperfectly  developed 
males  and  female.s,  3S0 

Thunbergia  alata,  90,  277,  331 

Tin  me,  419 

Tiuziiiami,  on  Solarium  tuberosum, 
362,  388 

Tobacco,  203 

Transmission  of  the  good  effects  of 
a  cro.-s  to  Jater  generations,  303 

Trees  separated  seXi-s,  411 

Trifoliuui  aroense,  367,  384 

incaruatum,  361 

minus,  368 

pratense,  361.  426,  434 

prociinibens,  368 

repens,  361 

Tropxolum  minus,  144 ;  measure- 
ment-, 145  ;  early  flowering  of 
cro.ss.  d,  293 ;  seeds,  316,  323 

tricolor,  427  ;  seeds,  323 

Tulips,  394 

Typha,  405 


Umbelliferx,  172 

Urban,  Ig.,  fertilisation  of  Medioago 
lupulina,  368 


482 


INDEX. 


VANDELLIA. 


V. 


Yandellia  nummularifolia,  90,  278 ; 
seeds,  315,  H22  ;  self-fertile,  369 

Yauilla,  secretion  of  nectar,  403 

Verbascum  hjehnitis,  89,  311,  309 

■ nigrum,  89.  3:;0,  3tl 

phceniceum,  330,  341,  364 

thapsus,     89 :     measurements, 

90;  self-fertile,  311,3  ,9 

Vcilot  on  Convolvulus  tricolor,  55; 
intercrossing  of  Nemophila,  183; 
of  Leptosiphon,  394 

Veronica  agrestis,  369 

chamvkdrys,  369 

■ Uedernefolia,  369 

Viciafaba,  360,  404 

hirsuta,  367 

sa^'ua,  367,  403,  404 

Victoria  regia,  365 

Villarsia  parnassifolia,  390 

Vilmorin  on  transmitting  character 
to  offspring,  451 

Vinca  major,  r>62 

rosea,  362 

Viola  canina,  357 

tricolor,   123;    measurements, 

126,  127 ;  superiority  of  crossed 
plants,  286,  289 :  period  of 
flowering,  292,  296;  effects  of 
cross-fertilisation,  304 ;  seeds, 
316,  325 ;  partially  sterile,  358  ; 
corolla  removed,  420 

Violacex,  123 

Viscaria  oculata,  130;  measure- 
ment,   132  ■    average  height  of 


ZEA. 

crossed  and  self-fertilised,  276 ; 
simultaneous  flowering,  295; 
seeds,  316,  323;  self -fertile,  367 


W. 

Wallace,  Mr.,  the  beaks  and  faces 

of  brush-tongned  lories  covered 

with  pollen,  371 
Wasps  attracted  by  Epipactis  lati- 

folia,  375 
Weights,   relative,  of  crossed  and 

self-fertilised    plants,   244.    283; 

and    period    of    germination    of 

seeds,  352-355 
Wither,  Mr.,  fertilisation  of  flowers 

with  their  own  pollen,  341 
WiLon,   A.  J.,   superior  vigour  of 

crossed     seedlings    in     Brassica 

campestris  ruta  baga,  353 
Wistaria  sinensis,  376,  427 


Y. 


Yucca  moth,  448 


Z. 

Zea  mays,  16,  233 ;  measurements, 
16-18,  234;  difference  of  height 
between  crossed  and  self-fertilise  d, 
288;  eariy  flowering  of  crossed, 
293 ;  self-fertile,  369 ;  prepotency 
of  other  pollen,  397 


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THE    ANCIENT    LIFE-HISTORY    OF    THE     EARTH. 

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historical  phase  of  palaeontology  it  will  be  indispensable  to  students,  whether 
specially  pursuing  geology  or  biology  ;  and  without  it  no  man  who  aspires  even  to 
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Professor  JOSEPH    LE   CONTE'S   WORKS. 

EVOLUTION     AND     ITS     RELATION     TO     RELIGIOUS 

THOUGHT.  By  Joseph  Le  Conte,  LL.  D.,  Professor  of  Geology 
and  Natural  History  in  the  University  of  California.  With  numer- 
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ary, and  most  of  it  so  technical,  that  even  very  intelligent  persons  have  still  very 
vague  ideas  on  the  subject.  I  have  attempted  to  give  (1)  a  very  concise  account 
of  what  we  mean  by  evolution,  (2)  an  outline  of  the  evidences  of  its  truth  drawn 
from  many  different  sources,  and  (S)  its  relation  to  fundamental  religious  beliefs." 
—Extract from  Preface. 

ELEMENTS  OF  GEOLOGY.  A  Text-book  for  Colleges  and  for 
the  General  Reader.  By  Joseph  Le  Conte,  LL.  D.  With  upward 
of  900  Illustrations.    New  and  enlarged  edition.    8vo.    Cloth,  $4.00. 

"Besides  preparing  a  comprehensive  test-hook,  suited  to  present  demands, 
Professor  Le  Conte  has  given  us  a  volume  of  great  value  as  an  exposition  of  the 
subject,  thoroughly  up  to  date.  The  examples  and  applications  of  the  work  are 
almost  entirely  derived  from  this  country,  so  that  it  may  he  properly  considered 
an  American  geology.  We  can  commend  this  work  without  qualification  to  all 
who  desire  an  intelligent  acquaintance  with  geological  science,  as  fresh,  lucid, 
full,  authentic,  the  result  of  devoted  study  and.  of  long  experience  in  teaching." 
— Popular  Science  Monthly. 

RELIGION  AND  SCIENCE.  A  Series  of  Sunday  Lectures  on  the 
Relation  of  Natural  and  Revealed  Religion,  or  the  Truths  revealed 
in  Nature  and  Scripture.  By  Joseph  Le  Conte,  LL.  D.  12mo. 
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those  who  desire  to  examine  closely  the  strong  foundations  on  which  the  Chris- 
tian faith  is  reared." — Boston  Journal. 


SIGHT  :  An  Exposition  of  the  Principles  of  Monocular  and  Binocular 
Vision.  By  Joseph  Le  Conte,  LL.  D.  With  Illustrations.  12mo. 
Cloth,  $1.50. 

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find  an  American  book  that  can  rank  with  the  very  best  of  foreign  books  on  this 
subject."—  The  Nation. 


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DR.  HENRY  MAUDSLEY'S   WORKS. 

BODY  AND  WILL:  Being  an  Essay  concerning  Will  in  its 
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Cloth,  $2.50. 

BODY  AND  MIND:  An  Inquiry  into  their  Connection  and  Mutual 
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Cloth,  $1.50. 

PHYSIOLOGY   AND    PATHOLOGY   OF   MIND: 

PHYSIOLOGY  OF  THE  MIND.  New  edition.  1  vol.,  12mo. 
Cloth,  $2.00.  Contents  :  Chapter  I.  On  the  Method  of  the  Study 
of  the  Mind.— II.  The  Mind  and  the  Nervous  System.— III.  The 
Spinal  Cord,  or  Tertiary  Nervous  Centres ;  or,  Nervous  Centres 
of  Reflex  Action. — IV.  Secondary  Nervous  Centres ;  or,  Sensory 
Ganglia ;  Sensorium  Commune. — V.  Hemispherical  Ganglia ;  Cortical 
Cells  of  the  Cerebral  Hemispheres  ;  Ideational  Nervous  Centres, 
Primary  Nervous  Centres;  Intellectorium  Commune. — VI.  The 
Emotions. — VII.  Volition. — VIII. — Motor  Nei'vous  Centres,  or  Mo- 
torium  Commune  and  Actuation  or  Effeetion. — IX.  Memory  and 
Imagination. 

PATHOLOGY  OF  THE  MIND.  Being  the  Third  Edition  of 
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recast,  enlarged,  and  rewritten.  1  vol.,  12mo.  Cloth,  $2.00.  Con- 
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Insanity:  (A)  Etiological. — IV.  The  same  continued. — V.  The 
Causation  and  Prevention  of  Insanity :  (B)  Pathological. — VI.  The 
Insanity  of  Early  Life. — VII.  The  Symptomatology  of  Insanity. — 
VIII.  The  same  continued. — IX.  Clinical  Groups  of  Mental  Dis- 
ease.— X.  The  Morbid  Anatomy  of  Mental  Derangement. — XI.  The 
Treatment  of  Mental  Disorders. 

RESPONSIBILITY  IN  MENTAL  DISEASE.  (International 
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of  the  most  difficult  and  at  the  same  time  one  of  the  most  important  subjects  of  in- 
vestigation at  the  present  day." — New  York  Observer. 

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GEORGE   J.   ROMANES'S  WORKS. 

MENTAL   EVOLUTION   IN   MAN :    Origin  of  Human  Faculty. 
One  vol.,  8vo.     Cloth,  $3.00. 

*  This  work,  which  follows  "Mental  Evolution  in  Animals,"  by  the  same  au= 
'shor,  considers  the  probable  mode  of  genesis  of  the  human  mind  from  the  mind 
of  lower  animals,  and  attempts  to  show  that  there  is  no  distinction  of  kind  be- 
tween man  and  brute,  but,  on  the  contrary,  that  such  distinctions  as  do  exist  all 
admit  of  being  explained,  with  respect  to  their  evolution,  by  adequate  psycho- 
logical analysis. 

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Saturday  Review. 

JELLY-FISH,  STAR-FISH,  AND  SEA-URCHINS.     Being 

a  Research  on  Primitive  Nervous  Systems.     12rno.     Cloth,  $1.75. 

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reader,  I  have  also  sought  to  render  the  book  of  service  to  the  working  physi- 
ologist, by  bringing  together  in  one  consecutive  account  all  the  more  important 
observations  and  results  which  have  been  yielded  by  this  research." — Extract 
from  Preface. 

"A  profound  research  into  the  laws  of  primitive  nervous  systems  conducted 
by  one  of  the  ablest  English  investigators.  Mr.  Romanes  set  up  a  tent  on  the 
beach  and  examined  his  beautiful  pets  for  six  summers  in  succession.  Such 
patient  and  loving  work  has  borne  its  fruits  in  a  monograph  which  leaves  noth- 
ing to  be  said  about  jelly-fish,  star-fish,  and  sea-urchins.  Every  one  who  has 
studied  the  lowest  forms  of  life  on  the  sea-shore  admires  these  objects.  But  few 
have  any  idea  of  the  exquisite  delicacy  of  their  structure  and  their  nice  adapta- 
tion to  their  place  in  nature.  Mr.  Romanes  brings  out  the  subtile  beauties  of 
the  rudimentary  organisms,  and  shows  the  re.-emblances  they  bear  to  the  higher 
types  of  creation.  His  explanations  are  made  more  clear  by  a  large  number  of 
illustrations." — New  York  Journal  of  Commerce. 

ANIMAL   INTELLIGENCE.     12mo.     Cloth,  $1.75. 

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the  first  attempt  to  present  systematically  the  well-assured  results  of  observa- 
tion on  the  mental  life  of  animals."— Saturday  Review. 

MENTAL   EVOLUTION   IN   ANIMALS.     With  a  Posthumous 

Essay  od  Instinct,  by  Charles  Darwin.     12mo.     Cloth,  $2.00. 

"Mr.  "Romanes  has  followed  up  his  careful  enumeration  of  the  facts  of  'Ani- 
mal Intelligence,'  contributed  to  the  'International  Scientific  Series,'  with  a 
work  dealing  with  the  successive  stages  at  which  the  various  mental  phenomena 
appear  in  the  scale  of  life.  The  present  installment  displays  the  eime  evidence 
of  industry  in  collecting  facts  and  caution  in  co-ordinating  them  bj  theory  as  the 
former." — The  Athenceum. 


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ERNST    HAECKEL'S  WORKS. 

fHE  HISTORY  OF  CREATION;  OR,  TIIE  DEVELOP* 
MENT  OF  THE  EARTH  AND  ITS  INHABITANTS  BY  THE 
ACTION  OF  NATURAL  CAUSES.  A  Popular  Exposition  of  the 
Doctrine  of  Evolution  in  general,  and  of  that  of  Darwin,  Goethe, 
and  Lamarck  in  particular.  From  the  German  of  Ernst  Haeckel, 
Professor  in  the  University  of  Jena.  The  translation  revised  by 
Professor  E.  Ray  Lankester,  M.  A.,  F.  R.  S.,  Fellow  of  Exeter  Col- 
lege, Oxford.  Illustrated  with  Lithographic  Plates.  In  two  vols., 
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THE  EVOLUTION  OF  MAN.  A  Popular  Exposition  of  the 
Principal  Points  of  Human  Ontogeny  and  Phylogeny.  From  the 
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evolution,  in  its  application  to  the  history  of  man.  It  is  in  Germany,  be- 
yond any  other  European  country,  that  the  impulse  given  by  Darwin 
twenty  years  ago  to  the  theory  of  evolution  has  influenced  the  whole 
tenor  of  philosophical  opinion.  There  may  be,  and  are,  differences  in 
the  degree  to  which  the  doctrine  may  be  held  capable  of  extension  into 
the  domain  of  mind  and  morals ;  but  there  is  no  denying,  in  scientific 
circles  at  least,  that  as  regards  the  physical  history  of  organic  nature 
much  has  been  done  toward  making  good  a  continuous  scheme  of  being." 
—London  Saturday  Review. 

FREEDOM  IN  SCIENCE  AND  TEACHING.  From  the 
German  of  Ernst  Haeckel.  With  a  Prefatory  Note  by  T.  H. 
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Professor  E.    L.   YOUMANS'S  WORKS. 

THE     HAND-BOOK     OF     HOUSEHOLD     SCIENCE.     A 

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their  Scientific  Principles  and  Domestic  Applications.  12mo.  Illus- 
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THE  CULTURE  DEMANDED  BY  MODERN  LIFE. 
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Education.  Edited,  with  an  Introduction  on  Mental  Discipline  in 
Education.     1  vol.,  12mo.     Cloth,  $2.00. 

CORRELATION    AND    CONSERVATION    OF    FORCES. 

A  Series  of  Expositions  by  Scientific  Men.  Edited,  with  an  Intro- 
duction and  Brief  Biographical  Notices  of  the  Chief  Promoters  of 
the  New  Views,  by  Edward  L.  Youmans,  M.  D.  12mo.  Cloth, 
$2.00. 

CONTENTS. 
I.  By  Professor  W.  K.  Grove.     The  Correlation  of  Physical  Forces. 
II.  By  Professor  Helmholtz.     The  Interaction  of  Natural  Forces. 
III.  By  Dr.  J.  R.  Mayer.     1.  Remarks  on  the  Forces  of  Inorganic  Nature, 

2.  On  Celestial  Dynamics. 

3.  On  the  Mechanical  Equivalent  of  Heat. 
TV.  By  Dr.  Faraday.     Some  Thoughts  on  the  Conservation  of  Forces. 

V.  By  Professor  Liebxg.     The  Connection  and  Equivalence  of  Forces. 

VI.  By  Dr.  Carpenter.      The   Correlation  of  the   Physical   and  Vital 

Forces. 

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highest  law  in  physical  science,  the  principle  of  the  conservation  of  force. 
Sufficient  attention  has  not  been  paid  to  the  publication  of  collected  mono- 
graphs or  memoirs  upon  special  subjects.  Dr.  Youmans's  work  exhibits 
the  value  of  such  collections  in  a  very  striking  manner,  and  we  earnestly 
hope  his  excellent  example  may  be  followed  in  other  branches  of  science." 
American  Journal  of  Science. 


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OUTINGS  AT  ODD  TIMES.  By  Charles  C.  Abbott, 
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NATURALIST 'S  RAMBLES  ABOUT  HOME. 
By  Charles  C.  Abbott.     i2mo.    Cloth,  $1.50. 

"  The  home  about  which  Dr.  Abbott  rambles  is  clearly  the  haunt  of  fowl  and  fish, 
of  animal  and  insect  life  ;  and  it  is  of  the  habits  and  natuie  of  these  that  he  discourses 
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" '  Days  out  of  Doors '  is  a  series  of  sketches  of  animal  life  by  Charles  C.  Abbott, 
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now.  The  essays  and  narratives  in  this  book  are  grouped  in  twelve  chapters,  named 
after  the  months  of  the  year.  Under  'January  '  the  author  talks  of  squirrels,  musk- 
rats,  water-snakes,  and  the  predatory  animals  that  withstand  the  rigor  of  winter; 
under  '  February  '  of  frogs  and  herons,  crows  and  blackbirds ;  under  '  March '  of  gulls 
and  fishes  and  foxy  sparrows,  and  so  on  appropriately,  instructively,  and  divertingly 
through  the  whole  twelve." — The  New  York  Sun. 

*Y^HE  PLAYTIME  NATURALIST.      By  Dr.  J.  E. 
■*■        Taylor,  F.  L.  S.,  editor  of  "  Science  Gossip."     With  366  Illus- 
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